diff --git a/brain-bar/Sources/BrainBar/BrainBarServer.swift b/brain-bar/Sources/BrainBar/BrainBarServer.swift
index d1ccdfe5..b6611598 100644
--- a/brain-bar/Sources/BrainBar/BrainBarServer.swift
+++ b/brain-bar/Sources/BrainBar/BrainBarServer.swift
@@ -150,6 +150,7 @@ final class BrainBarServer: @unchecked Sendable {
     struct ClientState {
         var source: DispatchSourceRead
         var framing: MCPFraming
+        let paletteSession: MCPRouter.PaletteSession
         /// Whether this client uses Content-Length framing (LSP-style).
         /// false = newline-delimited JSON-RPC (Claude Code v2.1+).
         var usesContentLengthFraming: Bool = true
@@ -441,7 +442,11 @@ final class BrainBarServer: @unchecked Sendable {
         }
         readSource.resume()
 
-        clients[clientFD] = ClientState(source: readSource, framing: MCPFraming())
+        clients[clientFD] = ClientState(
+            source: readSource,
+            framing: MCPFraming(),
+            paletteSession: router.makePaletteSession()
+        )
         NSLog("[BrainBar] Client connected (fd: %d)", clientFD)
         debugLog("CLIENT CONNECTED fd=\(clientFD) (total clients: \(clients.count))")
     }
@@ -493,16 +498,29 @@ final class BrainBarServer: @unchecked Sendable {
     }
 
     private func handleMessage(fd: Int32, request: [String: Any]) -> [String: Any] {
+        let paletteSession = clients[fd]?.paletteSession
         if let toolCall = parseToolCall(request) {
             switch toolCall.name {
             case "brain_subscribe":
+                guard let paletteSession,
+                      router.isToolExposed(toolCall.name, session: paletteSession) else {
+                    return router.handle(request, session: paletteSession)
+                }
                 return handleSubscribeTool(fd: fd, id: request["id"], arguments: toolCall.arguments)
             case "brain_unsubscribe":
+                guard let paletteSession,
+                      router.isToolExposed(toolCall.name, session: paletteSession) else {
+                    return router.handle(request, session: paletteSession)
+                }
                 return handleUnsubscribeTool(fd: fd, id: request["id"], arguments: toolCall.arguments)
             case "brain_ack":
+                guard let paletteSession,
+                      router.isToolExposed(toolCall.name, session: paletteSession) else {
+                    return router.handle(request, session: paletteSession)
+                }
                 return handleAckTool(id: request["id"], arguments: toolCall.arguments)
             default:
-                let response = router.handle(request)
+                let response = router.handle(request, session: paletteSession)
                 if toolCall.name == "brain_store", !isToolError(response) {
                     publishStoredChunks(response: response, arguments: toolCall.arguments)
                 }
@@ -520,7 +538,7 @@ final class BrainBarServer: @unchecked Sendable {
                 break
             }
         }
-        return router.handle(request)
+        return router.handle(request, session: paletteSession)
     }
 
     @discardableResult
diff --git a/brain-bar/Sources/BrainBar/MCPRouter.swift b/brain-bar/Sources/BrainBar/MCPRouter.swift
index c1f7d9ad..c7f57078 100644
--- a/brain-bar/Sources/BrainBar/MCPRouter.swift
+++ b/brain-bar/Sources/BrainBar/MCPRouter.swift
@@ -10,6 +10,32 @@
 import Foundation
 
 final class MCPRouter: @unchecked Sendable {
+    private enum ToolProfile {
+        case core
+        case full
+    }
+
+    private static let profileEnvironmentKey = "BRAINLAYER_MCP_PROFILE"
+    private static let coreToolNames: Set<String> = [
+        "brain_search",
+        "brain_store",
+        "brain_recall",
+        "brain_expand",
+    ]
+    private static let coreToolDescriptions: [String: String] = [
+        "brain_search": "Search memory.",
+        "brain_store": "Store memory.",
+        "brain_recall": "Recall context.",
+        "brain_expand": "Expand chunk.",
+    ]
+    nonisolated(unsafe) private static let expandPaletteToolDefinition: [String: Any] = [
+        "name": "expand_palette",
+        "description": "Expose all tools.",
+        "inputSchema": [
+            "type": "object",
+        ] as [String: Any],
+    ]
+
     // Keep contested MCP writes interactive: make one short attempt, then queue
     // for replay so brain_store returns well under the 1s prompt-queue budget.
     // Longer contention handling belongs in the deferred single-writer/backpressure
@@ -29,6 +55,25 @@ final class MCPRouter: @unchecked Sendable {
     private static let pendingStoreDrainInitialDelay: TimeInterval = 0.25
     private static let pendingStoreDrainMaxDelay: TimeInterval = 30.0
 
+    final class PaletteSession: @unchecked Sendable {
+        private let lock = NSLock()
+        private var expanded = false
+
+        func isExpanded() -> Bool {
+            lock.lock()
+            defer { lock.unlock() }
+            return expanded
+        }
+
+        func expand() -> Bool {
+            lock.lock()
+            defer { lock.unlock() }
+            guard !expanded else { return false }
+            expanded = true
+            return true
+        }
+    }
+
     private struct ToolOutput {
         let text: String
         let metadata: [String: Any]
@@ -94,6 +139,8 @@ final class MCPRouter: @unchecked Sendable {
     private let hybridSearchClient: HybridSearchClientProtocol?
     private let dbPath: String?
     private let hybridSearchBudget: TimeInterval
+    private let toolProfile: ToolProfile
+    private let defaultPaletteSession = PaletteSession()
     let entityCache = EntityCache()
     private static let defaultStringMaxLength = 256
     private static let defaultStringArrayMaxItems = 100
@@ -121,15 +168,108 @@ final class MCPRouter: @unchecked Sendable {
     ]
 
     init(
+        profile: String? = nil,
         hybridSearchClient: HybridSearchClientProtocol? = nil,
         hybridSearchBudget: TimeInterval = 0.8,
         dbPath: String? = nil
     ) {
+        self.toolProfile = Self.resolveToolProfile(profile)
         self.hybridSearchClient = hybridSearchClient
         self.hybridSearchBudget = max(0.001, hybridSearchBudget)
         self.dbPath = dbPath
     }
 
+    private static func resolveToolProfile(_ explicitProfile: String?) -> ToolProfile {
+        let environmentProfile = ProcessInfo.processInfo.environment[profileEnvironmentKey]
+        let rawProfile = explicitProfile ?? environmentProfile
+        let normalized = rawProfile?
+            .trimmingCharacters(in: .whitespacesAndNewlines)
+            .lowercased() ?? ""
+
+        switch normalized {
+        case "full", "operator":
+            return .full
+        case "", "core":
+            return .core
+        default:
+            if explicitProfile == nil, let rawProfile = environmentProfile {
+                let message = "BrainBar: unknown \(profileEnvironmentKey)=\(rawProfile); using core profile\n"
+                FileHandle.standardError.write(Data(message.utf8))
+            }
+            return .core
+        }
+    }
+
+    func makePaletteSession() -> PaletteSession {
+        PaletteSession()
+    }
+
+    private func exposedToolDefinitions(for session: PaletteSession) -> [[String: Any]] {
+        if toolProfile == .full || session.isExpanded() {
+            return Self.toolDefinitions
+        }
+
+        let coreDefinitions = Self.toolDefinitions.filter { definition in
+            guard let name = definition["name"] as? String else { return false }
+            return Self.coreToolNames.contains(name)
+        }.map(Self.compactCoreToolDefinition)
+        return coreDefinitions + [Self.expandPaletteToolDefinition]
+    }
+
+    func isToolExposed(_ name: String, session: PaletteSession) -> Bool {
+        exposedToolDefinitions(for: session).contains { ($0["name"] as? String) == name }
+    }
+
+    private static func compactCoreToolDefinition(_ definition: [String: Any]) -> [String: Any] {
+        guard let name = definition["name"] as? String else { return definition }
+
+        var compact: [String: Any] = ["name": name]
+        compact["description"] = coreToolDescriptions[name]
+        if let inputSchema = definition["inputSchema"] as? [String: Any] {
+            compact["inputSchema"] = removingDescriptions(from: inputSchema)
+        }
+        return compact
+    }
+
+    private static func removingDescriptions(from value: Any) -> Any {
+        if let dictionary = value as? [String: Any] {
+            return dictionary.reduce(into: [String: Any]()) { result, entry in
+                guard entry.key != "description" else { return }
+                result[entry.key] = removingDescriptions(from: entry.value)
+            }
+        }
+        if let array = value as? [Any] {
+            return array.map(removingDescriptions(from:))
+        }
+        return value
+    }
+
+    private func expandPalette(session: PaletteSession) -> ToolOutput {
+        guard session.expand() else {
+            return ToolOutput(
+                text: "BrainLayer tool palette is already expanded.",
+                metadata: [
+                    "expanded": false,
+                    "already_expanded": true,
+                    "registered_tools": [String](),
+                ]
+            )
+        }
+
+        let deferredNames = Self.toolDefinitions.compactMap { definition -> String? in
+            guard let name = definition["name"] as? String else { return nil }
+            return Self.coreToolNames.contains(name) ? nil : name
+        }
+        return ToolOutput(
+            text: "Expanded BrainLayer tool palette.",
+            metadata: [
+                "expanded": true,
+                "already_expanded": false,
+                "registered_tools": deferredNames,
+            ]
+        )
+    }
+
     /// Inject database for tool handlers + load entity cache.
     func setDatabase(_ db: BrainDatabase) {
         setDatabases(write: db, read: db)
@@ -160,7 +300,8 @@ final class MCPRouter: @unchecked Sendable {
 
     /// Handle a parsed JSON-RPC request and return a response.
     /// Returns empty dict for notifications (no id).
-    func handle(_ request: [String: Any]) -> [String: Any] {
+    func handle(_ request: [String: Any], session: PaletteSession? = nil) -> [String: Any] {
+        let paletteSession = session ?? defaultPaletteSession
         guard let method = request["method"] as? String else {
             return jsonRPCError(id: request["id"], code: -32600, message: "Invalid request: missing method")
         }
@@ -181,9 +322,13 @@ final class MCPRouter: @unchecked Sendable {
             // If a client sends this with an id, ack it so it doesn't hang.
             return jsonRPCResult(id: id, result: [:] as [String: Any])
         case "tools/list":
-            return handleToolsList(id: id)
+            return handleToolsList(id: id, session: paletteSession)
         case "tools/call":
-            return handleToolsCall(id: id, params: request["params"] as? [String: Any] ?? [:])
+            return handleToolsCall(
+                id: id,
+                params: request["params"] as? [String: Any] ?? [:],
+                session: paletteSession
+            )
         case "resources/list":
             return handleResourcesList(id: id)
         case "prompts/list":
@@ -204,7 +349,7 @@ final class MCPRouter: @unchecked Sendable {
             "result": [
                 "protocolVersion": "2024-11-05",
                 "capabilities": [
-                    "tools": ["listChanged": false],
+                    "tools": ["listChanged": true],
                     "experimental": [
                         "claude/channel": [:] as [String: Any]
                     ]
@@ -219,12 +364,12 @@ final class MCPRouter: @unchecked Sendable {
 
     // MARK: - tools/list
 
-    private func handleToolsList(id: Any) -> [String: Any] {
+    private func handleToolsList(id: Any, session: PaletteSession) -> [String: Any] {
         return [
             "jsonrpc": "2.0",
             "id": id,
             "result": [
-                "tools": Self.toolDefinitions
+                "tools": exposedToolDefinitions(for: session)
             ]
         ]
     }
@@ -236,15 +381,22 @@ final class MCPRouter: @unchecked Sendable {
 
     // MARK: - tools/call
 
-    private func handleToolsCall(id: Any, params: [String: Any]) -> [String: Any] {
+    private func handleToolsCall(id: Any, params: [String: Any], session: PaletteSession) -> [String: Any] {
         guard let toolName = params["name"] as? String else {
             return jsonRPCError(id: id, code: -32602, message: "Missing tool name")
         }
 
         let arguments = params["arguments"] as? [String: Any] ?? [:]
 
+        if toolName == "expand_palette" {
+            guard toolProfile == .core else {
+                return jsonRPCError(id: id, code: -32601, message: "Unknown tool: \(toolName)")
+            }
+            return toolCallResult(id: id, output: expandPalette(session: session))
+        }
+
         // Check tool exists
-        guard Self.toolDefinitions.contains(where: { ($0["name"] as? String) == toolName }) else {
+        guard isToolExposed(toolName, session: session) else {
             return jsonRPCError(id: id, code: -32601, message: "Unknown tool: \(toolName)")
         }
 
@@ -252,19 +404,7 @@ final class MCPRouter: @unchecked Sendable {
         do {
             try Self.validate(arguments: arguments, for: toolName)
             let output = try dispatchTool(name: toolName, arguments: arguments)
-            var result: [String: Any] = [
-                "content": [
-                    ["type": "text", "text": output.text]
-                ]
-            ]
-            for (key, value) in output.metadata {
-                result[key] = value
-            }
-            return [
-                "jsonrpc": "2.0",
-                "id": id,
-                "result": result
-            ]
+            return toolCallResult(id: id, output: output)
         } catch {
             return [
                 "jsonrpc": "2.0",
@@ -279,6 +419,22 @@ final class MCPRouter: @unchecked Sendable {
         }
     }
 
+    private func toolCallResult(id: Any, output: ToolOutput) -> [String: Any] {
+        var result: [String: Any] = [
+            "content": [
+                ["type": "text", "text": output.text]
+            ]
+        ]
+        for (key, value) in output.metadata {
+            result[key] = value
+        }
+        return [
+            "jsonrpc": "2.0",
+            "id": id,
+            "result": result,
+        ]
+    }
+
     private func dispatchTool(name: String, arguments: [String: Any]) throws -> ToolOutput {
         switch name {
         case "brain_search":
diff --git a/brain-bar/Tests/BrainBarTests/MCPRouterTests.swift b/brain-bar/Tests/BrainBarTests/MCPRouterTests.swift
index 27291e4d..60419d55 100644
--- a/brain-bar/Tests/BrainBarTests/MCPRouterTests.swift
+++ b/brain-bar/Tests/BrainBarTests/MCPRouterTests.swift
@@ -58,6 +58,27 @@ private func collectStringArrays(in schema: [String: Any], path: String = "") ->
 }
 
 final class MCPRouterTests: XCTestCase {
+    private static let coreToolNames = [
+        "brain_search",
+        "brain_store",
+        "brain_recall",
+        "brain_expand",
+        "expand_palette",
+    ]
+
+    private func listedTools(_ router: MCPRouter) -> [[String: Any]] {
+        let response = router.handle([
+            "jsonrpc": "2.0",
+            "id": 2,
+            "method": "tools/list",
+        ])
+        return (response["result"] as? [String: Any])?["tools"] as? [[String: Any]] ?? []
+    }
+
+    private func listedToolNames(_ router: MCPRouter) -> [String] {
+        listedTools(router).compactMap { $0["name"] as? String }
+    }
+
     private func assertDeferredBrainStoreReceipt(
         _ result: [String: Any],
         chunkID: String,
@@ -88,7 +109,7 @@ final class MCPRouterTests: XCTestCase {
     // MARK: - Initialize
 
     func testInitializeReturnsProtocolVersion() throws {
-        let router = MCPRouter()
+        let router = MCPRouter(profile: "full")
         let request: [String: Any] = [
             "jsonrpc": "2.0",
             "id": 1,
@@ -109,7 +130,8 @@ final class MCPRouterTests: XCTestCase {
 
         // Must declare tool capabilities
         let capabilities = result?["capabilities"] as? [String: Any]
-        XCTAssertNotNil(capabilities?["tools"])
+        let tools = capabilities?["tools"] as? [String: Any]
+        XCTAssertEqual(tools?["listChanged"] as? Bool, true)
         XCTAssertNil(capabilities?["resources"], "Tag resources should not be advertised during initialize")
         let experimental = capabilities?["experimental"] as? [String: Any]
         XCTAssertEqual((experimental?["claude/channel"] as? [String: Any])?.isEmpty, true)
@@ -123,7 +145,7 @@ final class MCPRouterTests: XCTestCase {
 
         try db.insertChunk(id: "tagged-1", content: "Tagged chunk", sessionId: "s1", project: "test", contentType: "assistant_text", importance: 5, tags: "[\"agent-message\"]")
 
-        let router = MCPRouter()
+        let router = MCPRouter(profile: "full")
         router.setDatabase(db)
 
         let response = router.handle([
@@ -140,8 +162,75 @@ final class MCPRouterTests: XCTestCase {
 
     // MARK: - Tools list
 
+    func testCoreProfilesExposeOnlyCoreFourAndExpansionControl() throws {
+        XCTAssertEqual(listedToolNames(MCPRouter(profile: "core")), Self.coreToolNames)
+        for profile in ["", "   ", "core", "bogus"] {
+            XCTAssertEqual(listedToolNames(MCPRouter(profile: profile)), Self.coreToolNames)
+        }
+    }
+
+    func testEnvironmentProfileControlsDefaultRouter() throws {
+        let environmentKey = "BRAINLAYER_MCP_PROFILE"
+        let originalProfile = ProcessInfo.processInfo.environment[environmentKey]
+        defer {
+            if let originalProfile {
+                setenv(environmentKey, originalProfile, 1)
+            } else {
+                unsetenv(environmentKey)
+            }
+        }
+
+        setenv(environmentKey, "operator", 1)
+        let canonicalNames = MCPRouter.toolDefinitions.compactMap { $0["name"] as? String }
+        XCTAssertEqual(listedToolNames(MCPRouter()), canonicalNames)
+
+        setenv(environmentKey, "core", 1)
+        XCTAssertEqual(listedToolNames(MCPRouter()), Self.coreToolNames)
+    }
+
+    func testFullAndOperatorProfilesPreserveCanonicalInventory() throws {
+        let canonicalNames = MCPRouter.toolDefinitions.compactMap { $0["name"] as? String }
+
+        XCTAssertEqual(canonicalNames.count, 17)
+        XCTAssertEqual(listedToolNames(MCPRouter(profile: "full")), canonicalNames)
+        XCTAssertEqual(listedToolNames(MCPRouter(profile: "operator")), canonicalNames)
+    }
+
+    func testCoreToolsListStaysWithinBootBudget() throws {
+        let tools = listedTools(MCPRouter(profile: "core"))
+        let data = try JSONSerialization.data(withJSONObject: tools, options: [.sortedKeys])
+
+        XCTAssertLessThanOrEqual(data.count, 1_500)
+    }
+
+    func testCorePaletteExpandsOnceAndDispatchesDeferredTools() throws {
+        let router = MCPRouter(profile: "core")
+
+        XCTAssertEqual(listedToolNames(router), Self.coreToolNames)
+        let deferredBeforeExpansion = router.handle(toolCall(id: 20, name: "brain_tags", arguments: [:]))
+        XCTAssertEqual((deferredBeforeExpansion["error"] as? [String: Any])?["code"] as? Int, -32601)
+
+        let firstExpansion = router.handle(toolCall(id: 21, name: "expand_palette", arguments: [:]))
+        let firstResult = try XCTUnwrap(firstExpansion["result"] as? [String: Any])
+        XCTAssertEqual(firstResult["expanded"] as? Bool, true)
+        XCTAssertEqual(firstResult["already_expanded"] as? Bool, false)
+        XCTAssertEqual((firstResult["registered_tools"] as? [String])?.count, 13)
+        XCTAssertEqual(listedToolNames(router), MCPRouter.toolDefinitions.compactMap { $0["name"] as? String })
+
+        let deferredAfterExpansion = router.handle(toolCall(id: 22, name: "brain_tags", arguments: [:]))
+        XCTAssertNil(deferredAfterExpansion["error"])
+        XCTAssertNotNil(deferredAfterExpansion["result"])
+
+        let secondExpansion = router.handle(toolCall(id: 23, name: "expand_palette", arguments: [:]))
+        let secondResult = try XCTUnwrap(secondExpansion["result"] as? [String: Any])
+        XCTAssertEqual(secondResult["expanded"] as? Bool, false)
+        XCTAssertEqual(secondResult["already_expanded"] as? Bool, true)
+        XCTAssertEqual(secondResult["registered_tools"] as? [String], [])
+        XCTAssertEqual(listedToolNames(router).count, 17)
+    }
+
     func testToolsListReturnsAllTools() throws {
-        let router = MCPRouter()
+        let router = MCPRouter(profile: "full")
         let request: [String: Any] = [
             "jsonrpc": "2.0",
             "id": 2,
@@ -167,7 +256,7 @@ final class MCPRouterTests: XCTestCase {
     }
 
     func testEncodedToolsListEnvelopeStartsWithJSONRPC() throws {
-        let router = MCPRouter()
+        let router = MCPRouter(profile: "full")
         let response = router.handle([
             "jsonrpc": "2.0",
             "id": 2,
@@ -185,7 +274,7 @@ final class MCPRouterTests: XCTestCase {
     }
 
     func testToolsListPreservesCanonicalAnnotations() throws {
-        let router = MCPRouter()
+        let router = MCPRouter(profile: "full")
         let response = router.handle([
             "jsonrpc": "2.0",
             "id": 2,
@@ -204,7 +293,7 @@ final class MCPRouterTests: XCTestCase {
     }
 
     func testEachToolHasInputSchema() throws {
-        let router = MCPRouter()
+        let router = MCPRouter(profile: "full")
         let request: [String: Any] = [
             "jsonrpc": "2.0",
             "id": 3,
@@ -222,7 +311,7 @@ final class MCPRouterTests: XCTestCase {
     }
 
     func testEachToolHasExpectedAnnotations() throws {
-        let router = MCPRouter()
+        let router = MCPRouter(profile: "full")
         let response = router.handle([
             "jsonrpc": "2.0",
             "id": 3,
@@ -315,7 +404,7 @@ final class MCPRouterTests: XCTestCase {
     // MARK: - Tools call
 
     func testToolsCallDispatchesToHandler() throws {
-        let router = MCPRouter()
+        let router = MCPRouter(profile: "full")
         let request: [String: Any] = [
             "jsonrpc": "2.0",
             "id": 4,
@@ -363,7 +452,7 @@ final class MCPRouterTests: XCTestCase {
                 ]
             )
         )
-        let router = MCPRouter(hybridSearchClient: helper)
+        let router = MCPRouter(profile: "full", hybridSearchClient: helper)
         router.setDatabase(db)
 
         let response = router.handle([
@@ -422,7 +511,7 @@ final class MCPRouterTests: XCTestCase {
 
         let helperText = "python helper canonical KG/search output"
         let helper = RecordingHybridSearchClient(response: HybridSearchResponse(text: helperText))
-        let router = MCPRouter(hybridSearchClient: helper)
+        let router = MCPRouter(profile: "full", hybridSearchClient: helper)
         router.setDatabase(db)
 
         let response = router.handle([
@@ -460,7 +549,7 @@ final class MCPRouterTests: XCTestCase {
         )
 
         let helper = RecordingHybridSearchClient()
-        let router = MCPRouter(hybridSearchClient: helper)
+        let router = MCPRouter(profile: "full", hybridSearchClient: helper)
         router.setDatabase(db)
 
         let response = router.handle([
@@ -506,7 +595,7 @@ No results found.
 """
             )
         )
-        let router = MCPRouter(hybridSearchClient: helper)
+        let router = MCPRouter(profile: "full", hybridSearchClient: helper)
         router.setDatabase(db)
 
         let response = router.handle(toolCall(id: 179, name: "brain_search", arguments: [
@@ -527,7 +616,7 @@ No results found.
         let db = BrainDatabase(path: tempDB)
         defer { db.close() }
 
-        let router = MCPRouter()
+        let router = MCPRouter(profile: "full")
         router.setDatabase(db)
         let fullContent = "Sensitive full content must not be echoed in the MCP store response"
 
@@ -574,7 +663,7 @@ No results found.
         )
 
         let helper = RecordingHybridSearchClient()
-        let router = MCPRouter(hybridSearchClient: helper)
+        let router = MCPRouter(profile: "full", hybridSearchClient: helper)
         router.setDatabase(db)
 
         let response = router.handle([
@@ -625,7 +714,7 @@ No results found.
         XCTAssertEqual(try sqlitePragma(handle: readDB.dbHandle, name: "busy_timeout"), "250")
         writeDB.close()
 
-        let router = MCPRouter()
+        let router = MCPRouter(profile: "full")
         router.setDatabases(write: writeDB, read: readDB)
 
         let searchText = try toolText(router.handle(toolCall(id: 301, name: "brain_search", arguments: [
@@ -684,7 +773,7 @@ No results found.
             sql: "UPDATE chunks SET summary = 'Short generated summary' WHERE id = 'expand-full-target'"
         )
 
-        let router = MCPRouter()
+        let router = MCPRouter(profile: "full")
         router.setDatabase(db)
         let expandText = try toolText(router.handle(toolCall(id: 307, name: "brain_expand", arguments: [
             "chunk_id": "expand-full-target"
@@ -725,7 +814,7 @@ No results found.
         // here and failed with SQLITE_READONLY.
         XCTAssertEqual(try sqlitePragma(handle: readDB.dbHandle, name: "query_only"), "1")
 
-        let router = MCPRouter()
+        let router = MCPRouter(profile: "full")
         router.setDatabases(write: writeDB, read: readDB)
 
         let response = router.handle(toolCall(id: 401, name: "brain_search", arguments: [
@@ -768,7 +857,7 @@ No results found.
             response: HybridSearchResponse(text: "slow helper should not win"),
             delay: 0.50
         )
-        let router = MCPRouter(hybridSearchClient: helper, hybridSearchBudget: 0.05)
+        let router = MCPRouter(profile: "full", hybridSearchClient: helper, hybridSearchBudget: 0.05)
         router.setDatabases(write: writeDB, read: readDB)
 
         let started = Date()
@@ -803,7 +892,7 @@ No results found.
             response: HybridSearchResponse(text: "helper should not be called while warming")
         )
         helper.ready = false
-        let router = MCPRouter(hybridSearchClient: helper)
+        let router = MCPRouter(profile: "full", hybridSearchClient: helper)
         router.setDatabase(db)
 
         let response = router.handle(toolCall(id: 308, name: "brain_search", arguments: [
@@ -836,7 +925,7 @@ No results found.
         let helper = RecordingHybridSearchClient(
             response: HybridSearchResponse(text: "helper should not be called")
         )
-        let router = MCPRouter(hybridSearchClient: helper)
+        let router = MCPRouter(profile: "full", hybridSearchClient: helper)
         router.setDatabase(db)
         let response = router.handle([
             "jsonrpc": "2.0",
@@ -875,7 +964,7 @@ No results found.
         }
         try sqliteExec(path: tempDB, sql: "DELETE FROM chunks_fts_trigram")
 
-        let router = MCPRouter()
+        let router = MCPRouter(profile: "full")
         router.setDatabase(db)
 
         let response = router.handle([
@@ -910,7 +999,7 @@ No results found.
         defer { db.close() }
         try sqliteExec(path: tempDB, sql: "DROP TABLE IF EXISTS chunks_fts_trigram")
 
-        let router = MCPRouter()
+        let router = MCPRouter(profile: "full")
         router.setDatabase(db)
 
         let response = router.handle([
@@ -933,7 +1022,7 @@ No results found.
     }
 
     func testToolsCallUnknownToolReturnsError() throws {
-        let router = MCPRouter()
+        let router = MCPRouter(profile: "full")
         let request: [String: Any] = [
             "jsonrpc": "2.0",
             "id": 5,
@@ -952,7 +1041,7 @@ No results found.
     }
 
     func testBrainDigestRejectsOversizedContentAtSchemaLayer() throws {
-        let router = MCPRouter()
+        let router = MCPRouter(profile: "full")
         let response = router.handle([
             "jsonrpc": "2.0",
             "id": 6,
@@ -975,7 +1064,7 @@ No results found.
     }
 
     func testBrainDigestSchemaExposesProjectAndTitle() throws {
-        let router = MCPRouter()
+        let router = MCPRouter(profile: "full")
         let response = router.handle([
             "jsonrpc": "2.0",
             "id": 7,
@@ -999,7 +1088,7 @@ No results found.
         let db = BrainDatabase(path: tempDB)
         defer { db.close() }
 
-        let router = MCPRouter()
+        let router = MCPRouter(profile: "full")
         router.setDatabase(db)
         let response = router.handle([
             "jsonrpc": "2.0",
@@ -1025,7 +1114,7 @@ No results found.
     }
 
     func testBrainSubscribeToolIsServerHandled() throws {
-        let router = MCPRouter()
+        let router = MCPRouter(profile: "full")
         let request: [String: Any] = [
             "jsonrpc": "2.0",
             "id": 7,
@@ -1045,7 +1134,7 @@ No results found.
     }
 
     func testBrainUnsubscribeToolIsServerHandled() throws {
-        let router = MCPRouter()
+        let router = MCPRouter(profile: "full")
         let request: [String: Any] = [
             "jsonrpc": "2.0",
             "id": 8,
@@ -1064,7 +1153,7 @@ No results found.
     }
 
     func testBrainAckToolIsServerHandled() throws {
-        let router = MCPRouter()
+        let router = MCPRouter(profile: "full")
         let request: [String: Any] = [
             "jsonrpc": "2.0",
             "id": 9,
@@ -1086,7 +1175,7 @@ No results found.
     // MARK: - Unknown method
 
     func testUnknownMethodReturnsError() throws {
-        let router = MCPRouter()
+        let router = MCPRouter(profile: "full")
         let request: [String: Any] = [
             "jsonrpc": "2.0",
             "id": 6,
@@ -1111,7 +1200,7 @@ No results found.
         try db.insertChunk(id: "f-1", content: "Socket handling code", sessionId: "s1", project: "brainbar", contentType: "assistant_text", importance: 5)
         try db.insertChunk(id: "f-2", content: "Socket connection code", sessionId: "s2", project: "other-proj", contentType: "assistant_text", importance: 5)
 
-        let router = MCPRouter()
+        let router = MCPRouter(profile: "full")
         router.setDatabase(db)
         let response = router.handle([
             "jsonrpc": "2.0",
@@ -1142,7 +1231,7 @@ No results found.
 
         try db.insertChunk(id: "detail-1", content: "Socket handling code", sessionId: "s1", project: "brainbar", contentType: "assistant_text", importance: 5)
 
-        let router = MCPRouter()
+        let router = MCPRouter(profile: "full")
         router.setDatabase(db)
         let response = router.handle([
             "jsonrpc": "2.0",
@@ -1172,7 +1261,7 @@ No results found.
         try db.insertChunk(id: "i-1", content: "Critical security finding", sessionId: "s1", project: "test", contentType: "assistant_text", importance: 9)
         try db.insertChunk(id: "i-2", content: "Security review notes", sessionId: "s2", project: "test", contentType: "assistant_text", importance: 3)
 
-        let router = MCPRouter()
+        let router = MCPRouter(profile: "full")
         router.setDatabase(db)
         let response = router.handle([
             "jsonrpc": "2.0",
@@ -1204,7 +1293,7 @@ No results found.
         _ = try db.store(content: "Sagit meeting notes", tags: ["meeting"], importance: 6, source: "whatsapp")
         _ = try db.store(content: "Sagit meeting notes", tags: ["meeting"], importance: 6, source: "youtube")
 
-        let router = MCPRouter()
+        let router = MCPRouter(profile: "full")
         router.setDatabase(db)
         let response = router.handle([
             "jsonrpc": "2.0",
@@ -1242,7 +1331,7 @@ No results found.
             importance: 8
         )
 
-        let router = MCPRouter()
+        let router = MCPRouter(profile: "full")
         router.setDatabase(db)
         let response = router.handle([
             "jsonrpc": "2.0",
@@ -1279,7 +1368,7 @@ No results found.
         try db.insertEntity(id: "tool-1", type: "tool", name: "Claude Code")
         try db.insertRelation(sourceId: "proj-1", targetId: "tool-1", relationType: "used_by")
 
-        let router = MCPRouter()
+        let router = MCPRouter(profile: "full")
         router.setDatabase(db)
         let response = router.handle([
             "jsonrpc": "2.0",
@@ -1310,7 +1399,7 @@ No results found.
         try db.insertChunk(id: "s-1", content: "Search result one", sessionId: "session-1", project: "brainlayer", contentType: "assistant_text", importance: 5)
         try db.insertChunk(id: "s-2", content: "Search result two", sessionId: "session-2", project: "orchestrator", contentType: "user_message", importance: 4)
 
-        let router = MCPRouter()
+        let router = MCPRouter(profile: "full")
         router.setDatabase(db)
         let response = router.handle([
             "jsonrpc": "2.0",
@@ -1345,7 +1434,7 @@ No results found.
             timestamp: "2026-03-31T04:03:00.000Z"
         )
 
-        let router = MCPRouter()
+        let router = MCPRouter(profile: "full")
         router.setDatabase(db)
         let response = router.handle([
             "jsonrpc": "2.0",
@@ -1382,7 +1471,7 @@ No results found.
         }
         try db.acknowledge(agentID: "agent-1", seq: readSeq)
 
-        let router = MCPRouter()
+        let router = MCPRouter(profile: "full")
         router.setDatabase(db)
         let response = router.handle([
             "jsonrpc": "2.0",
@@ -1416,7 +1505,7 @@ No results found.
         defer { db.close() }
 
         try db.insertChunk(id: "archive-target", content: "Archive this stale memory", sessionId: "s1", project: "test", contentType: "assistant_text", importance: 5)
-        let router = MCPRouter()
+        let router = MCPRouter(profile: "full")
         router.setDatabase(db)
 
         let archiveResponse = router.handle([
@@ -1454,7 +1543,7 @@ No results found.
 
         try db.insertChunk(id: "old-chunk", content: "TechGym guidance old version", sessionId: "s1", project: "test", contentType: "assistant_text", importance: 5)
         try db.insertChunk(id: "new-chunk", content: "TechGym guidance new version", sessionId: "s2", project: "test", contentType: "assistant_text", importance: 9)
-        let router = MCPRouter()
+        let router = MCPRouter(profile: "full")
         router.setDatabase(db)
 
         let supersedeResponse = router.handle([
@@ -1510,7 +1599,7 @@ No results found.
         try db.insertChunk(id: "mem-sagit-1", content: "Sagit Stern gave the TechGym lecture about search ranking.", sessionId: "s1", project: "test", contentType: "assistant_text", importance: 8)
         try db.linkEntityChunk(entityId: "person-sagit", chunkId: "mem-sagit-1", relevance: 0.9)
 
-        let router = MCPRouter()
+        let router = MCPRouter(profile: "full")
         router.setDatabase(db)
         let response = router.handle([
             "jsonrpc": "2.0",
@@ -1544,7 +1633,7 @@ No results found.
             importance: 5
         )
 
-        let router = MCPRouter()
+        let router = MCPRouter(profile: "full")
         router.setDatabase(db)
         let enrichResponse = router.handle([
             "jsonrpc": "2.0",
@@ -1597,7 +1686,7 @@ No results found.
         )
         db.exec("UPDATE chunks SET enrich_status = 'duplicate' WHERE id = 'enrich-duplicate'")
 
-        let router = MCPRouter()
+        let router = MCPRouter(profile: "full")
         router.setDatabase(db)
         let response = router.handle([
             "jsonrpc": "2.0",
@@ -1630,7 +1719,7 @@ No results found.
             importance: 5
         )
 
-        let router = MCPRouter()
+        let router = MCPRouter(profile: "full")
         router.setDatabase(db)
         let response = router.handle([
             "jsonrpc": "2.0",
@@ -1662,7 +1751,7 @@ No results found.
             importance: 5
         )
 
-        let router = MCPRouter()
+        let router = MCPRouter(profile: "full")
         router.setDatabase(db)
         let response = router.handle([
             "jsonrpc": "2.0",
@@ -1688,7 +1777,7 @@ No results found.
 
         let dbPath = tempDir.appendingPathComponent("brainbar.db").path
         let queuePath = tempDir.appendingPathComponent("pending-stores.jsonl")
-        let router = MCPRouter(dbPath: dbPath)
+        let router = MCPRouter(profile: "full", dbPath: dbPath)
 
         let response = router.handle([
             "jsonrpc": "2.0",
@@ -1744,7 +1833,7 @@ No results found.
         let db = BrainDatabase(path: dbPath)
         db.close()
 
-        let router = MCPRouter(dbPath: dbPath)
+        let router = MCPRouter(profile: "full", dbPath: dbPath)
         router.setDatabase(db)
 
         let response = router.handle([
@@ -1802,7 +1891,7 @@ No results found.
         defer { db.close() }
         db.failNextStoreWithBusyForTesting = true
 
-        let router = MCPRouter()
+        let router = MCPRouter(profile: "full")
         router.setDatabase(db)
 
         let response = router.handle([
@@ -1876,7 +1965,7 @@ No results found.
             }
         }
 
-        let router = MCPRouter()
+        let router = MCPRouter(profile: "full")
         router.setDatabase(db)
 
         let started = Date()
@@ -1937,7 +2026,7 @@ No results found.
             }
         }
 
-        let router = MCPRouter()
+        let router = MCPRouter(profile: "full")
         router.setDatabase(db)
 
         let queuedContent = "Queued current write should drain after the writer lock clears"
@@ -1994,7 +2083,7 @@ No results found.
         defer { db.close() }
         db.failNextStoreWithBusyForTesting = true
 
-        let router = MCPRouter()
+        let router = MCPRouter(profile: "full")
         router.setDatabase(db)
 
         let queuedContent = "Queued current write survives one unreadable pending store queue snapshot"
@@ -2056,7 +2145,7 @@ No results found.
         let db = BrainDatabase(path: dbPath)
         defer { db.close() }
 
-        let router = MCPRouter()
+        let router = MCPRouter(profile: "full")
         router.setDatabase(db)
 
         let response = router.handle([
@@ -2108,7 +2197,7 @@ No results found.
         defer { db.close() }
         db.failNextStoreWithBusyForTesting = true
 
-        let router = MCPRouter()
+        let router = MCPRouter(profile: "full")
         router.setDatabase(db)
 
         let response = router.handle([
@@ -2171,7 +2260,7 @@ No results found.
         let db = BrainDatabase(path: dbPath)
         defer { db.close() }
 
-        let router = MCPRouter()
+        let router = MCPRouter(profile: "full")
         router.setDatabase(db)
 
         let response = router.handle([
@@ -2225,7 +2314,7 @@ No results found.
         let db = BrainDatabase(path: dbPath)
         defer { db.close() }
 
-        let router = MCPRouter()
+        let router = MCPRouter(profile: "full")
         router.setDatabase(db)
 
         let response = router.handle([
@@ -2505,7 +2594,7 @@ No results found.
     // MARK: - Notifications (no id)
 
     func testNotificationDoesNotRequireResponse() {
-        let router = MCPRouter()
+        let router = MCPRouter(profile: "full")
         let request: [String: Any] = [
             "jsonrpc": "2.0",
             "method": "notifications/initialized",
diff --git a/brain-bar/Tests/BrainBarTests/SocketIntegrationTests.swift b/brain-bar/Tests/BrainBarTests/SocketIntegrationTests.swift
index 03963134..2929e00d 100644
--- a/brain-bar/Tests/BrainBarTests/SocketIntegrationTests.swift
+++ b/brain-bar/Tests/BrainBarTests/SocketIntegrationTests.swift
@@ -12,9 +12,12 @@ final class SocketIntegrationTests: XCTestCase {
     var server: BrainBarServer!
     var db: BrainDatabase!
     var tempDBPath: String!
+    var originalMCPProfile: String?
 
     override func setUp() {
         super.setUp()
+        originalMCPProfile = ProcessInfo.processInfo.environment["BRAINLAYER_MCP_PROFILE"]
+        setenv("BRAINLAYER_MCP_PROFILE", "full", 1)
         tempDBPath = NSTemporaryDirectory() + "brainbar-integration-\(UUID().uuidString).db"
         db = BrainDatabase(path: tempDBPath)
         server = BrainBarServer(socketPath: testSocketPath, dbPath: tempDBPath, database: db)
@@ -28,6 +31,11 @@ final class SocketIntegrationTests: XCTestCase {
         try? FileManager.default.removeItem(atPath: tempDBPath)
         try? FileManager.default.removeItem(atPath: tempDBPath + "-wal")
         try? FileManager.default.removeItem(atPath: tempDBPath + "-shm")
+        if let originalMCPProfile {
+            setenv("BRAINLAYER_MCP_PROFILE", originalMCPProfile, 1)
+        } else {
+            unsetenv("BRAINLAYER_MCP_PROFILE")
+        }
         super.tearDown()
     }
 
@@ -111,6 +119,74 @@ final class SocketIntegrationTests: XCTestCase {
         }
     }
 
+    func testCorePaletteExpansionIsIsolatedPerSocketClient() throws {
+        restartServer(profile: "core")
+        let firstFD = try connectClient()
+        defer { close(firstFD) }
+        let secondFD = try connectClient()
+        defer { close(secondFD) }
+        try initializeClient(fd: firstFD, name: "first-core-client")
+        try initializeClient(fd: secondFD, name: "second-core-client")
+
+        let coreNames: Set<String> = [
+            "brain_search", "brain_store", "brain_recall", "brain_expand", "expand_palette",
+        ]
+        XCTAssertEqual(Set(try listedToolNames(on: firstFD, id: 2)), coreNames)
+        XCTAssertEqual(Set(try listedToolNames(on: secondFD, id: 2)), coreNames)
+
+        try sendMCPRequest(on: firstFD, request: [
+            "jsonrpc": "2.0", "id": 3, "method": "tools/call",
+            "params": ["name": "expand_palette", "arguments": [:] as [String: Any]],
+        ])
+        let expansion = try readMCPMessage(fd: firstFD)
+        XCTAssertEqual((expansion["result"] as? [String: Any])?["expanded"] as? Bool, true)
+
+        XCTAssertEqual(try listedToolNames(on: firstFD, id: 4).count, 17)
+        XCTAssertEqual(Set(try listedToolNames(on: secondFD, id: 3)), coreNames)
+    }
+
+    func testCoreProfileRejectsServerHandledToolsUntilExpansion() throws {
+        restartServer(profile: "core")
+        let fd = try connectClient()
+        defer { close(fd) }
+        try initializeClient(fd: fd, name: "core-subscription-client")
+
+        let serverHandledTools: [(name: String, arguments: [String: Any])] = [
+            ("brain_subscribe", ["agent_id": "core-agent", "tags": ["agent-message"]]),
+            ("brain_unsubscribe", ["agent_id": "core-agent", "tags": ["agent-message"]]),
+            ("brain_ack", ["agent_id": "core-agent", "seq": 1]),
+        ]
+        for (offset, tool) in serverHandledTools.enumerated() {
+            try sendMCPRequest(on: fd, request: [
+                "jsonrpc": "2.0", "id": 2 + offset, "method": "tools/call",
+                "params": ["name": tool.name, "arguments": tool.arguments] as [String: Any],
+            ])
+            let deferred = try readMCPMessage(fd: fd)
+            XCTAssertEqual(
+                (deferred["error"] as? [String: Any])?["code"] as? Int,
+                -32601,
+                "\(tool.name) should stay deferred until this client expands its palette"
+            )
+        }
+
+        try sendMCPRequest(on: fd, request: [
+            "jsonrpc": "2.0", "id": 5, "method": "tools/call",
+            "params": ["name": "expand_palette", "arguments": [:] as [String: Any]],
+        ])
+        _ = try readMCPMessage(fd: fd)
+
+        try sendMCPRequest(on: fd, request: [
+            "jsonrpc": "2.0", "id": 6, "method": "tools/call",
+            "params": [
+                "name": "brain_subscribe",
+                "arguments": ["agent_id": "core-agent", "tags": ["agent-message"]] as [String: Any],
+            ],
+        ])
+        let expanded = try readMCPMessage(fd: fd)
+        XCTAssertNil(expanded["error"])
+        XCTAssertNotNil(expanded["result"])
+    }
+
     func testRawLineToolsListCompactsForClaudeExtensionLimit() throws {
         let fd = try connectClient()
         defer { close(fd) }
@@ -874,6 +950,23 @@ final class SocketIntegrationTests: XCTestCase {
 
     // MARK: - Helper
 
+    private func restartServer(profile: String) {
+        server.stop()
+        setenv("BRAINLAYER_MCP_PROFILE", profile, 1)
+        server = BrainBarServer(socketPath: testSocketPath, dbPath: tempDBPath, database: db)
+        server.start()
+        XCTAssertTrue(waitForSocket(at: testSocketPath), "Server should bind \(testSocketPath)")
+    }
+
+    private func listedToolNames(on fd: Int32, id: Int) throws -> [String] {
+        try sendMCPRequest(on: fd, request: [
+            "jsonrpc": "2.0", "id": id, "method": "tools/list",
+        ])
+        let response = try readMCPMessage(fd: fd)
+        let tools = (response["result"] as? [String: Any])?["tools"] as? [[String: Any]]
+        return tools?.compactMap { $0["name"] as? String } ?? []
+    }
+
     private func waitForSocket(at path: String, timeout: TimeInterval = 3.0) -> Bool {
         let deadline = Date().addingTimeInterval(timeout)
         while Date() < deadline {
diff --git a/contracts/engine-ui-contract.md b/contracts/engine-ui-contract.md
index 932f3062..e3a8d4c0 100644
--- a/contracts/engine-ui-contract.md
+++ b/contracts/engine-ui-contract.md
@@ -17,19 +17,31 @@ Pinned shared surfaces:
 
 ## 2. BrainBar MCP Router Over `/tmp/brainbar.sock`
 
-BrainBar is the MCP surface of record. Its router dispatches 17 tools at `brain-bar/Sources/BrainBar/MCPRouter.swift:195` and defines the tool schemas at `brain-bar/Sources/BrainBar/MCPRouter.swift:950`.
+BrainBar is the MCP surface of record. Its router keeps 17 canonical definitions and dispatch handlers in `brain-bar/Sources/BrainBar/MCPRouter.swift`.
 
 Canonical BrainBar tools:
 
 `brain_search`, `brain_store`, `brain_get_person`, `brain_recall`, `brain_entity`, `brain_digest`, `brain_update`, `brain_expand`, `brain_tags`, `brain_supersede`, `brain_archive`, `brain_enrich`, `brain_subscribe`, `brain_unsubscribe`, `brain_ack`, `brain_maintenance_rebuild_trigram`, `brain_backup_vacuum_into`.
 
-Python `src/brainlayer/mcp/` remains the secondary transport with 13 tools defined at `src/brainlayer/mcp/__init__.py:387`, `src/brainlayer/mcp/__init__.py:543`, `src/brainlayer/mcp/__init__.py:568`, `src/brainlayer/mcp/__init__.py:672`, `src/brainlayer/mcp/__init__.py:701`, `src/brainlayer/mcp/__init__.py:862`, `src/brainlayer/mcp/__init__.py:905`, `src/brainlayer/mcp/__init__.py:974`, `src/brainlayer/mcp/__init__.py:999`, `src/brainlayer/mcp/__init__.py:1042`, `src/brainlayer/mcp/__init__.py:1080`, `src/brainlayer/mcp/__init__.py:1113`, and `src/brainlayer/mcp/__init__.py:1135`.
+Python `src/brainlayer/mcp/` remains the secondary transport with 13 canonical definitions built by `_full_tool_definitions()` in `src/brainlayer/mcp/__init__.py`.
 
 Differences:
 
 - BrainBar-only: `brain_subscribe`, `brain_unsubscribe`, `brain_ack`, `brain_maintenance_rebuild_trigram`, `brain_backup_vacuum_into`.
 - Python-only: `brain_resume`.
 
+### MCP palette profiles
+
+Both transports resolve `BRAINLAYER_MCP_PROFILE` once per server session:
+
+- missing, blank, `core`, or an unknown value exposes `brain_search`, `brain_store`, `brain_recall`, `brain_expand`, and the `expand_palette` control tool;
+- `full` and `operator` expose the transport's complete canonical inventory and omit the redundant control;
+- unknown values fail closed to core rather than exposing operator tools.
+
+BrainBar's core declarations are compact projections of the canonical definitions: names and validation-relevant input-schema fields remain, verbose description/annotation metadata is omitted or shortened, and full/operator definitions stay byte-for-byte unchanged. Python core mode selects the existing `Tool` objects directly. Neither transport deletes or renames a canonical handler.
+
+Calling `expand_palette` in a core session exposes the complete inventory for subsequent `tools/list` and `tools/call` requests. The first receipt contains `expanded: true`, `already_expanded: false`, and the newly registered names; later calls are successful no-ops with `already_expanded: true`. BrainBar advertises `tools.listChanged = true`; clients refresh on the next `tools/list` because this router seam does not push a notification.
+
 ## 3. Hybrid Helper Subprocess And Socket
 
 BrainBar starts the helper from `HybridSearchHelperClient` with `-m brainlayer.brainbar_hybrid_helper --socket-path ... --db-path ...`; see the invocation at `brain-bar/Sources/BrainBar/HybridSearchHelperClient.swift:189`. If `pythonExecutable` resolves to `/usr/bin/env`, BrainBar invokes `python3`; otherwise it invokes the resolved Python executable directly.
diff --git a/docs/plans/2026-07-13-brainlayer-core4-palette-design.md b/docs/plans/2026-07-13-brainlayer-core4-palette-design.md
new file mode 100644
index 00000000..8979a518
--- /dev/null
+++ b/docs/plans/2026-07-13-brainlayer-core4-palette-design.md
@@ -0,0 +1,91 @@
+# BrainLayer Core-4 Palette Design
+
+## Goal
+
+Reduce the default BrainLayer MCP boot surface to the four tools that cover 98.62% of observed calls while preserving every existing handler and allowing a session to expose the full palette without reconnecting.
+
+## Context
+
+The live BrainLayer surface is BrainBar's 17-tool MCP router. The Python MCP server is a secondary transport with 13 tools, including the Python-only `brain_resume`. The measured live schema is 4,038 bytes / 1,027 `o200k_base` tokens; the four canonical schemas (`brain_search`, `brain_store`, `brain_recall`, `brain_expand`) are 1,263 bytes / 326 tokens before adding the small expansion control.
+
+Both transports therefore need the same profile semantics, but each keeps its existing canonical inventory and dispatch implementation.
+
+## Considered approaches
+
+### 1. Stateful per-session palette with one-shot expansion (chosen)
+
+Each server process resolves `BRAINLAYER_MCP_PROFILE` once at construction/import time. `core` lists the Core 4 plus `expand_palette`; `full` and `operator` list the transport's complete canonical inventory. BrainBar tracks expansion per socket client, while the Python stdio server has one module session. Calling `expand_palette` changes only that MCP session to full and makes its subsequent `tools/list` calls return the full inventory.
+
+This directly mirrors cmuxlayer's proven seam, meets the boot budget, and supports a mid-session upgrade. The trade-off is a small amount of instance state and a `tools/list_changed` capability declaration even though BrainBar does not currently push that notification.
+
+### 2. Reconnect-only profile switching
+
+Keep `tools/list` stateless and require a reconnect with `BRAINLAYER_MCP_PROFILE=full`. This is simpler but fails the explicit self-upgrade requirement.
+
+### 3. Advertise all tools with deferred metadata
+
+Return all schemas and mark non-core tools with `defer_loading`. This preserves direct calls but does not reduce the measured `tools/list` bytes, so it fails the primary acceptance gate.
+
+## Profile contract
+
+- `core` is the default when the environment variable is missing or blank.
+- `full` exposes the complete transport inventory.
+- `operator` is a documented alias of `full` for operator sessions.
+- Unknown profile values fail closed to `core` and log one warning; they never silently expose operator tools.
+- Profile resolution is per server session. Changing the process environment after construction does not mutate an existing session.
+
+The resident core is exactly:
+
+1. `brain_search`
+2. `brain_store`
+3. `brain_recall`
+4. `brain_expand`
+
+`expand_palette` is a control tool and is not counted as a BrainLayer domain tool. It appears only while the server is in an unexpanded core profile.
+
+## BrainBar design
+
+`MCPRouter` receives an optional profile override for deterministic tests and otherwise reads `BRAINLAYER_MCP_PROFILE` during initialization. It stores a boolean expanded state behind the router instance.
+
+`tools/list` derives compact core declarations from the immutable canonical `toolDefinitions` array and appends a minimal `expand_palette` definition. The projection keeps names and validation-relevant input-schema fields while removing verbose nested descriptions/annotations and shortening top-level descriptions. This was required because the current in-repo Core 4 serialized to 3,722 bytes even though the older live-front audit payload was 1,263 bytes. Full/operator selection returns all 17 canonical definitions byte-for-byte and omits the redundant control.
+
+`tools/call` validates against the currently exposed definitions. A deferred tool called before expansion receives the existing unknown-tool JSON-RPC error, including BrainBar's server-handled subscription tools. `expand_palette` is handled without touching the database, flips the client session once, and returns an idempotent structured receipt containing `expanded`, `already_expanded`, and the newly exposed names. Subsequent calls are successful no-ops. BrainBar keeps the expansion state in each `ClientState`; direct router users receive one router-local default session.
+
+`initialize` advertises `tools.listChanged = true` because the list can change during a session. BrainBar's request/response router has no server-push channel at this seam, so clients discover the new list on the next `tools/list`; the expansion response makes that contract explicit.
+
+## Python design
+
+The Python MCP module keeps one immutable full-tool builder and adds a small palette controller resolved from `BRAINLAYER_MCP_PROFILE`. The registered `list_tools` callback returns Core 4 plus `expand_palette` by default, or the existing 13-tool inventory for full/operator/expanded sessions.
+
+The existing `call_tool` branches remain intact. A profile exposure guard rejects deferred names before dispatch, while `expand_palette` updates only the module server session and returns the same idempotent receipt shape as BrainBar. No aliases are renamed or removed; Python-only `brain_resume` remains available in full/operator mode.
+
+## Compatibility and safety
+
+- No database, schema, migration, search, or write-path code changes.
+- No canonical tool definition or handler is deleted.
+- Core schemas are mechanically projected from the existing definitions, keeping validation-relevant fields tied to the canonical source while dropping only boot-cost metadata.
+- Full/operator output is contract-compatible with today's complete inventory.
+- `brain_expand` remains resident despite its Python deprecation notice because the live corpus and handoff explicitly require Core 4 for this release.
+- Unknown profiles fail closed to core.
+
+## Verification
+
+Tests will prove, on both transports:
+
+- missing/blank/`core` profiles list exactly Core 4 plus the control tool;
+- `full` and `operator` list the complete pre-change inventory;
+- invalid profiles fail closed;
+- deferred calls fail before expansion and dispatch after expansion;
+- expansion is idempotent and round-trips from core to full;
+- canonical definitions remain present and unchanged;
+- the serialized default BrainBar `tools` array stays below 1,500 bytes;
+- measured full and core bytes/tokens are reported with the same compact JSON and `o200k_base` method used by the audit.
+
+Focused Python and Swift tests run first, followed by the full non-live Python suite and the full BrainBar Swift suite. The final receipt records measured before/after bytes and token counts.
+
+## Non-goals
+
+- No Core-3 migration or folding `brain_expand` into `brain_search`.
+- No launcher, daemon, database, schema, or writer changes.
+- No deletion or renaming of compatibility tools.
+- No attempt to make profile changes affect other sessions in the same process.
diff --git a/docs/plans/2026-07-13-brainlayer-core4-palette.md b/docs/plans/2026-07-13-brainlayer-core4-palette.md
new file mode 100644
index 00000000..6be6494a
--- /dev/null
+++ b/docs/plans/2026-07-13-brainlayer-core4-palette.md
@@ -0,0 +1,304 @@
+# BrainLayer Core-4 Palette Implementation Plan
+
+> **For Claude:** REQUIRED SUB-SKILL: Use superpowers:executing-plans to implement this plan task-by-task.
+
+**Goal:** Make Core 4 the default BrainLayer MCP palette on BrainBar and Python, with full/operator overrides and an idempotent mid-session `expand_palette` upgrade.
+
+**Architecture:** Keep each transport's canonical tool definitions and dispatch handlers unchanged. Add a small stateful palette controller at each `tools/list`/`tools/call` seam; core sessions expose four domain tools plus a minimal expansion control, while full/operator sessions expose the pre-change complete inventory.
+
+**Tech Stack:** Swift 6/XCTest, Python 3.13/pytest, MCP JSON-RPC, compact JSON measurement, `tiktoken` `o200k_base`.
+
+---
+
+### Task 1: Pin BrainBar profile and budget behavior
+
+**Files:**
+- Modify: `brain-bar/Tests/BrainBarTests/MCPRouterTests.swift`
+- Modify: `brain-bar/Sources/BrainBar/MCPRouter.swift`
+
+**Step 1: Write the failing profile tests**
+
+Add tests that construct `MCPRouter(profile: ...)`, call `tools/list`, and assert:
+
+```swift
+let coreNames = ["brain_search", "brain_store", "brain_recall", "brain_expand", "expand_palette"]
+XCTAssertEqual(toolNames(router: MCPRouter(profile: nil)), coreNames)
+XCTAssertEqual(toolNames(router: MCPRouter(profile: "core")), coreNames)
+
+for profile in ["full", "operator"] {
+    XCTAssertEqual(toolNames(router: MCPRouter(profile: profile)).count, 17)
+}
+```
+
+Also cover blank and invalid profiles, asserting both fail closed to the same core list. Move existing canonical schema/annotation assertions to `MCPRouter.toolDefinitions` or a full-profile router so they continue to pin all 17 definitions.
+
+Serialize the core `tools` array with sorted compact JSON and assert `data.count <= 1_500`.
+
+**Step 2: Run the focused Swift tests and verify RED**
+
+Run:
+
+```bash
+cd brain-bar
+swift test --filter MCPRouterTests
+```
+
+Expected: compilation/test failures because `MCPRouter(profile:)` and palette filtering do not exist.
+
+**Step 3: Implement the minimal BrainBar profile controller**
+
+In `MCPRouter.swift`:
+
+- add `BRAINLAYER_MCP_PROFILE` resolution in `init`, with an optional explicit profile for tests;
+- represent `core`, `full`, and `operator` without modifying `toolDefinitions`;
+- add a lock-safe `PaletteSession`, use one router-local default for direct callers, and attach a distinct session to each BrainBar socket client;
+- compute compact core projections from the canonical Core 4 (preserving validation fields while dropping verbose descriptive metadata) plus a minimal control definition, or all 17 canonical definitions unchanged;
+- make `handleToolsList` return `exposedToolDefinitions`;
+- make the existing call guard validate against exposed definitions;
+- set `tools.listChanged` to true.
+
+Unknown and blank values resolve to core. Log a warning only for a nonblank unknown environment value.
+
+**Step 4: Run focused tests and verify GREEN**
+
+Run `cd brain-bar && swift test --filter MCPRouterTests`.
+
+Expected: all `MCPRouterTests` pass with zero failures.
+
+**Step 5: Commit the BrainBar profile seam**
+
+```bash
+git add brain-bar/Sources/BrainBar/MCPRouter.swift brain-bar/Tests/BrainBarTests/MCPRouterTests.swift
+git commit -m "feat: add BrainBar core4 MCP profile"
+```
+
+### Task 2: Add BrainBar expansion round-trip
+
+**Files:**
+- Modify: `brain-bar/Tests/BrainBarTests/MCPRouterTests.swift`
+- Modify: `brain-bar/Sources/BrainBar/MCPRouter.swift`
+
+**Step 1: Write failing expansion tests**
+
+Exercise one core router instance:
+
+```swift
+XCTAssertEqual(listedNames(router).count, 5)
+let first = call(router, name: "expand_palette")
+XCTAssertEqual(first["expanded"] as? Bool, true)
+XCTAssertEqual(listedNames(router).count, 17)
+let second = call(router, name: "expand_palette")
+XCTAssertEqual(second["already_expanded"] as? Bool, true)
+XCTAssertEqual(listedNames(router).count, 17)
+```
+
+Also prove a deferred no-database tool such as `brain_tags` receives `-32601` before expansion and reaches its existing handler after expansion (returning a normal tool result, even if that result reports missing database).
+
+**Step 2: Run focused tests and verify RED**
+
+Run `cd brain-bar && swift test --filter MCPRouterTests`.
+
+Expected: failure because the expansion control is listed but not dispatched and does not mutate the palette.
+
+**Step 3: Implement idempotent expansion**
+
+Handle `expand_palette` before canonical schema validation. On the first call, set `paletteExpanded = true` and return content plus top-level metadata:
+
+```swift
+[
+    "expanded": true,
+    "already_expanded": false,
+    "registered_tools": deferredNames,
+]
+```
+
+Later calls return `expanded: false`, `already_expanded: true`, and an empty registered list. The canonical switch and all 17 handlers remain unchanged.
+
+**Step 4: Run focused tests and verify GREEN**
+
+Run `cd brain-bar && swift test --filter MCPRouterTests`.
+
+Expected: all focused tests pass.
+
+**Step 5: Commit the expansion path**
+
+```bash
+git add brain-bar/Sources/BrainBar/MCPRouter.swift brain-bar/Tests/BrainBarTests/MCPRouterTests.swift
+git commit -m "feat: expand BrainBar palette in session"
+```
+
+### Task 3: Pin the Python palette contract
+
+**Files:**
+- Create: `tests/test_mcp_palette.py`
+- Create: `src/brainlayer/mcp/palette.py`
+- Modify: `src/brainlayer/mcp/__init__.py`
+
+**Step 1: Write failing controller and transport tests**
+
+Test a new `ToolPalette` directly and the MCP callbacks through an injected/reset palette fixture:
+
+```python
+CORE = {"brain_search", "brain_store", "brain_recall", "brain_expand", "expand_palette"}
+
+@pytest.mark.parametrize("profile", [None, "", "core", "bogus"])
+def test_core_profiles_fail_closed(profile):
+    palette = ToolPalette(profile)
+    assert {tool.name for tool in palette.expose(full_tools())} == CORE
+
+@pytest.mark.parametrize("profile", ["full", "operator"])
+def test_full_profiles_preserve_all_python_tools(profile):
+    assert len(ToolPalette(profile).expose(full_tools())) == 13
+```
+
+Add an async round-trip test proving the first expansion exposes all 13 tools, the second expansion is a no-op, and a deferred call is rejected before expansion.
+
+**Step 2: Run the focused Python tests and verify RED**
+
+Run:
+
+```bash
+pytest tests/test_mcp_palette.py -q
+```
+
+Expected: import/attribute failures because the palette controller does not exist.
+
+**Step 3: Implement the Python palette controller**
+
+Create `palette.py` with:
+
+- `PROFILE_ENV = "BRAINLAYER_MCP_PROFILE"`;
+- immutable Core 4 names;
+- normalized `core`/`full`/`operator` resolution with invalid fail-closed behavior;
+- `expose(full_tools)` that selects existing `Tool` objects and appends a minimal control in unexpanded core mode;
+- `is_exposed(name)` and idempotent `expand()` returning a receipt dictionary.
+
+Refactor the current literal `list_tools` body into `_full_tool_definitions()`. Keep the decorated callback thin:
+
+```python
+@server.list_tools()
+async def list_tools() -> list[Tool]:
+    return _tool_palette.expose(_full_tool_definitions())
+```
+
+At the start of `call_tool`, handle `expand_palette`, then reject other currently deferred names before entering the existing branch chain. Do not modify any existing handler body.
+
+**Step 4: Run focused tests and verify GREEN**
+
+Run `pytest tests/test_mcp_palette.py -q`.
+
+Expected: all palette tests pass.
+
+**Step 5: Run nearby Python contract tests**
+
+Run:
+
+```bash
+pytest tests/test_mcp_input_schema_limits.py tests/test_mcp_labeled_field_output.py tests/test_mcp_digest_modes.py tests/test_smart_search_entity_dedup.py -q
+```
+
+Expected: zero failures. Update tests that intentionally inspect the complete inventory to use the full profile fixture; do not weaken canonical schema assertions.
+
+**Step 6: Commit the Python seam**
+
+```bash
+git add src/brainlayer/mcp/__init__.py src/brainlayer/mcp/palette.py tests/test_mcp_palette.py tests/test_mcp_input_schema_limits.py tests/test_mcp_labeled_field_output.py tests/test_mcp_digest_modes.py tests/test_smart_search_entity_dedup.py
+git commit -m "feat: add Python core4 MCP profile"
+```
+
+### Task 4: Document parity and measure the palette
+
+**Files:**
+- Modify: `contracts/engine-ui-contract.md`
+- Create: `scripts/measure_mcp_palette.py`
+- Create: `tests/test_measure_mcp_palette.py`
+
+**Step 1: Write a failing measurement test**
+
+Add a pure helper test with a small fixed schema fixture. Assert compact JSON uses UTF-8 byte length and `o200k_base` tokens, and assert the live BrainBar core payload is at most 1,500 bytes.
+
+**Step 2: Run the measurement tests and verify RED**
+
+Run `pytest tests/test_measure_mcp_palette.py -q`.
+
+Expected: failure because the script/helper does not exist.
+
+**Step 3: Implement the measurement script**
+
+The script must accept JSON from a file/stdin, extract the `tools` array when given a JSON-RPC envelope, serialize with compact separators and sorted keys, and print exact bytes/tokens. Use `tiktoken.get_encoding("o200k_base")` and exit nonzero when `--max-bytes` is exceeded.
+
+**Step 4: Update the transport contract**
+
+Document:
+
+- `BRAINLAYER_MCP_PROFILE=core|full|operator`;
+- core default and its four domain names;
+- `expand_palette` semantics;
+- BrainBar's 17-tool and Python's 13-tool full inventories remain canonical;
+- profile state is per session and invalid values fail closed.
+
+**Step 5: Run tests and record measurements**
+
+Run:
+
+```bash
+pytest tests/test_measure_mcp_palette.py tests/test_mcp_palette.py -q
+cd brain-bar && swift test --filter MCPRouterTests
+```
+
+Generate compact full/core `tools` JSON for BrainBar and run the measurement script on both. Record exact before/after bytes and tokens for the receipt.
+
+**Step 6: Commit docs and measurement tooling**
+
+```bash
+git add contracts/engine-ui-contract.md scripts/measure_mcp_palette.py tests/test_measure_mcp_palette.py
+git commit -m "test: enforce BrainLayer palette budget"
+```
+
+### Task 5: Full verification and PR loop
+
+**Files:**
+- Modify: `~/Gits/orchestrator/docs.local/collab/driver-buddy-2026-07-12.md`
+
+**Step 1: Run complete local verification**
+
+Run fresh:
+
+```bash
+pytest tests/ -m "not integration and not live" --tb=short
+cd brain-bar && swift test
+git diff --check origin/main...HEAD
+```
+
+Read the complete summaries and report exact pass/fail/skip counts. Do not claim green from exit codes alone.
+
+**Step 2: Re-read the handoff and design acceptance gates**
+
+Verify line by line: Core 4 default, 13 deferred on BrainBar, full/operator override, mid-session expansion, no removal/rename, no DB/schema change, per-profile tests, <=1.5 KB core budget, exact measurements.
+
+**Step 3: Push and open a ready PR**
+
+```bash
+git push -u origin feat/core4-palette
+gh pr create --title "feat: add BrainLayer Core-4 MCP palette" --body-file <prepared-body>
+```
+
+The PR body includes the design, exact before/after bytes/tokens, test receipts, and risk note that only MCP exposure changes.
+
+**Step 4: Request required reviews**
+
+Post `@codex review`, `@cursor`, and `@bugbot` on the ready PR. Inspect CI with `gh pr checks --watch` and inspect all review threads. Fix or explicitly answer every actionable/high/critical item, with no more than three review rounds.
+
+**Step 5: Write completion receipts**
+
+Append to `~/Gits/orchestrator/docs.local/collab/driver-buddy-2026-07-12.md` under `@orc-driver-v2` with:
+
+- PR URL and head SHA;
+- exact full/core bytes and tokens;
+- local and CI test counts;
+- review status;
+- explicit note that DB/schema were untouched.
+
+Store the same milestone in BrainLayer with WHAT + WHY, then search it back to verify persistence. Stop at the handoff's worker endpoint (ready PR + reviews addressed); do not merge unless separately instructed.
+
+TASK_DONE
diff --git a/pyproject.toml b/pyproject.toml
index aecda2d7..c14fa9c5 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -82,6 +82,7 @@ dev = [
     "ruff>=0.1.0",
     "scikit-learn<1.6",
     "setuptools>=70.0.0,<81",
+    "tiktoken>=0.7.0",
     "umap-learn>=0.5.0",
 ]
 docs = [
diff --git a/scripts/measure_mcp_palette.py b/scripts/measure_mcp_palette.py
new file mode 100644
index 00000000..ae3471bf
--- /dev/null
+++ b/scripts/measure_mcp_palette.py
@@ -0,0 +1,74 @@
+#!/usr/bin/env python3
+"""Measure a compact MCP tools payload in UTF-8 bytes and o200k tokens."""
+
+from __future__ import annotations
+
+import argparse
+import json
+import sys
+from pathlib import Path
+from typing import Any
+
+import tiktoken
+
+
+def extract_tools(payload: Any) -> list[dict[str, Any]]:
+    """Extract a tools array from a raw list, result object, or JSON-RPC envelope."""
+    tools: Any
+    if isinstance(payload, list):
+        tools = payload
+    elif isinstance(payload, dict) and isinstance(payload.get("tools"), list):
+        tools = payload["tools"]
+    elif (
+        isinstance(payload, dict)
+        and isinstance(payload.get("result"), dict)
+        and isinstance(payload["result"].get("tools"), list)
+    ):
+        tools = payload["result"]["tools"]
+    else:
+        raise ValueError("Expected a tools array or a JSON-RPC result containing one")
+
+    if not all(isinstance(tool, dict) for tool in tools):
+        raise ValueError("Every tools entry must be a JSON object")
+    return tools
+
+
+def canonical_tools_json(tools: list[dict[str, Any]]) -> str:
+    return json.dumps(tools, ensure_ascii=False, separators=(",", ":"), sort_keys=True)
+
+
+def measure_tools(tools: list[dict[str, Any]]) -> dict[str, int]:
+    canonical = canonical_tools_json(tools)
+    return {
+        "tools": len(tools),
+        "bytes": len(canonical.encode("utf-8")),
+        "tokens": len(tiktoken.get_encoding("o200k_base").encode(canonical)),
+    }
+
+
+def _load_payload(path: str) -> Any:
+    if path == "-":
+        return json.load(sys.stdin)
+    with Path(path).open(encoding="utf-8") as handle:
+        return json.load(handle)
+
+
+def main(argv: list[str] | None = None) -> int:
+    parser = argparse.ArgumentParser(description=__doc__)
+    parser.add_argument("path", nargs="?", default="-", help="JSON file path, or - for stdin")
+    parser.add_argument("--max-bytes", type=int, help="Exit nonzero if the compact tools array exceeds this size")
+    args = parser.parse_args(argv)
+
+    try:
+        measurement = measure_tools(extract_tools(_load_payload(args.path)))
+    except (OSError, json.JSONDecodeError, ValueError) as exc:
+        parser.error(str(exc))
+
+    print(json.dumps(measurement, sort_keys=True))
+    if args.max_bytes is not None and measurement["bytes"] > args.max_bytes:
+        return 1
+    return 0
+
+
+if __name__ == "__main__":
+    raise SystemExit(main())
diff --git a/src/brainlayer/mcp/__init__.py b/src/brainlayer/mcp/__init__.py
index 84c72aa8..342e6b4d 100644
--- a/src/brainlayer/mcp/__init__.py
+++ b/src/brainlayer/mcp/__init__.py
@@ -1,6 +1,7 @@
 """BrainLayer MCP Server - Model Context Protocol interface for Claude Code."""
 
 import asyncio
+import json
 import logging
 import os
 from copy import deepcopy
@@ -40,6 +41,7 @@
 from .enrich_handler import _brain_enrich
 from .entity_handler import _brain_entity as _brain_entity
 from .entity_handler import _brain_get_person
+from .palette import EXPAND_TOOL_NAME, ToolPalette
 from .search_handler import (
     _brain_recall,
     _brain_resume,
@@ -396,9 +398,8 @@ def _apply_input_limits(node: Any, field_name: str | None = None) -> None:
 # --- Tool registration ---
 
 
-@server.list_tools()
-async def list_tools() -> list[Tool]:
-    """List available tools — 3 primary + backward-compat aliases."""
+def _full_tool_definitions() -> list[Tool]:
+    """Build the complete canonical Python MCP tool inventory."""
     return [
         Tool(
             name="brain_search",
@@ -1251,6 +1252,16 @@ async def list_tools() -> list[Tool]:
     ]
 
 
+_tool_palette = ToolPalette()
+_FULL_TOOL_NAMES = tuple(tool.name for tool in _full_tool_definitions())
+
+
+@server.list_tools()
+async def list_tools() -> list[Tool]:
+    """List tools exposed by this server session's palette."""
+    return _tool_palette.expose(_full_tool_definitions())
+
+
 # --- Completions ---
 
 
@@ -1319,6 +1330,18 @@ async def handle_completion(ref, argument) -> CompleteResult:
 async def call_tool(name: str, arguments: dict[str, Any]):
     """Handle tool calls — 3 primary tools + backward-compat aliases."""
 
+    if name == EXPAND_TOOL_NAME:
+        if _tool_palette.is_full:
+            return _error_result(f"Unknown tool: {name}")
+        receipt = _tool_palette.expand(_FULL_TOOL_NAMES)
+        return CallToolResult(
+            content=[TextContent(type="text", text=json.dumps(receipt, sort_keys=True))],
+            structuredContent=receipt,
+        )
+
+    if name in _FULL_TOOL_NAMES and not _tool_palette.is_exposed(name):
+        return _error_result(f"Tool not exposed in the core profile: {name}. Call {EXPAND_TOOL_NAME} first.")
+
     # --- New consolidated tools ---
 
     if name == "brain_search":
diff --git a/src/brainlayer/mcp/palette.py b/src/brainlayer/mcp/palette.py
new file mode 100644
index 00000000..88cc5f55
--- /dev/null
+++ b/src/brainlayer/mcp/palette.py
@@ -0,0 +1,71 @@
+"""Per-session MCP tool palette selection."""
+
+from __future__ import annotations
+
+import logging
+import os
+from collections.abc import Sequence
+
+from mcp.types import Tool
+
+PROFILE_ENV = "BRAINLAYER_MCP_PROFILE"
+CORE_TOOL_NAMES = (
+    "brain_search",
+    "brain_store",
+    "brain_recall",
+    "brain_expand",
+)
+EXPAND_TOOL_NAME = "expand_palette"
+
+logger = logging.getLogger(__name__)
+
+
+class ToolPalette:
+    """Resolve one MCP session's visible tools and expansion state."""
+
+    def __init__(self, profile: str | None = None) -> None:
+        environment_profile = os.environ.get(PROFILE_ENV)
+        raw_profile = environment_profile if profile is None else profile
+        normalized = (raw_profile or "").strip().lower()
+
+        self._full = normalized in {"full", "operator"}
+        self._expanded = False
+        if normalized not in {"", "core", "full", "operator"} and profile is None:
+            logger.warning("Unknown %s=%r; using core profile", PROFILE_ENV, environment_profile)
+
+    @property
+    def is_full(self) -> bool:
+        return self._full
+
+    def expose(self, full_tools: Sequence[Tool]) -> list[Tool]:
+        if self._full or self._expanded:
+            return list(full_tools)
+
+        tools_by_name = {tool.name: tool for tool in full_tools}
+        core_tools = [tools_by_name[name] for name in CORE_TOOL_NAMES if name in tools_by_name]
+        core_tools.append(
+            Tool(
+                name=EXPAND_TOOL_NAME,
+                description="Expose all tools.",
+                inputSchema={"type": "object"},
+            )
+        )
+        return core_tools
+
+    def is_exposed(self, name: str) -> bool:
+        return self._full or self._expanded or name in CORE_TOOL_NAMES or name == EXPAND_TOOL_NAME
+
+    def expand(self, full_tool_names: Sequence[str]) -> dict[str, object]:
+        if self._expanded:
+            return {
+                "expanded": False,
+                "already_expanded": True,
+                "registered_tools": [],
+            }
+
+        self._expanded = True
+        return {
+            "expanded": True,
+            "already_expanded": False,
+            "registered_tools": [name for name in full_tool_names if name not in CORE_TOOL_NAMES],
+        }
diff --git a/tests/test_3tool_aliases.py b/tests/test_3tool_aliases.py
index ccc4a2d1..c6788065 100644
--- a/tests/test_3tool_aliases.py
+++ b/tests/test_3tool_aliases.py
@@ -14,8 +14,20 @@
 import asyncio
 from unittest.mock import AsyncMock, MagicMock, patch
 
+import pytest
+
 from brainlayer.mcp.search_handler import _brain_recall, _smart_detect_mode
 
+
+@pytest.fixture(autouse=True)
+def _use_full_palette_for_legacy_contracts(monkeypatch):
+    """This module verifies handlers retained behind the explicit full profile."""
+    import brainlayer.mcp as mcp_server
+    from brainlayer.mcp.palette import ToolPalette
+
+    monkeypatch.setattr(mcp_server, "_tool_palette", ToolPalette("full"))
+
+
 # ── Smart Mode Detection ─────────────────────────────────────────────────────
 
 
diff --git a/tests/test_audit_search_quality.py b/tests/test_audit_search_quality.py
index 227da0eb..28157ce6 100644
--- a/tests/test_audit_search_quality.py
+++ b/tests/test_audit_search_quality.py
@@ -122,9 +122,9 @@ async def test_mcp_recall_enum_matches_canonical(self):
 
     async def test_mcp_entity_enum_matches_canonical(self):
         """brain_entity entity_type enum must match the MCP schema contract."""
-        from brainlayer.mcp import list_tools
+        from brainlayer.mcp import _full_tool_definitions
 
-        tools = await list_tools()
+        tools = _full_tool_definitions()
         entity_tool = next(t for t in tools if t.name == "brain_entity")
         schema = entity_tool.inputSchema
         mcp_enum = schema["properties"]["entity_type"]["enum"]
diff --git a/tests/test_entity_type_sync.py b/tests/test_entity_type_sync.py
index e0ad4d36..6db6c289 100644
--- a/tests/test_entity_type_sync.py
+++ b/tests/test_entity_type_sync.py
@@ -28,12 +28,10 @@ def store(tmp_path):
 
 
 def _get_brain_entity_tool():
-    """Extract the brain_entity Tool object from the MCP server tool list."""
-    import asyncio
+    """Extract brain_entity from the explicit full-profile tool definitions."""
+    from brainlayer.mcp import _full_tool_definitions
 
-    from brainlayer.mcp import list_tools
-
-    tools = asyncio.run(list_tools())
+    tools = _full_tool_definitions()
     for tool in tools:
         if tool.name == "brain_entity":
             return tool
diff --git a/tests/test_mcp_digest_modes.py b/tests/test_mcp_digest_modes.py
index 11cbf3b4..63032dba 100644
--- a/tests/test_mcp_digest_modes.py
+++ b/tests/test_mcp_digest_modes.py
@@ -1,6 +1,5 @@
 """Tests for brain_digest MCP mode routing."""
 
-import asyncio
 from types import SimpleNamespace
 from unittest.mock import MagicMock
 
@@ -80,9 +79,9 @@ async def test_brain_digest_missing_content_with_mode_digest_errors():
 
 
 def test_brain_digest_input_schema_includes_mode_and_limit():
-    from brainlayer.mcp import list_tools
+    from brainlayer.mcp import _full_tool_definitions
 
-    tools = asyncio.run(list_tools())
+    tools = _full_tool_definitions()
     digest = next(t for t in tools if t.name == "brain_digest")
     props = digest.inputSchema["properties"]
 
diff --git a/tests/test_mcp_input_schema_limits.py b/tests/test_mcp_input_schema_limits.py
index f554b128..967cd36c 100644
--- a/tests/test_mcp_input_schema_limits.py
+++ b/tests/test_mcp_input_schema_limits.py
@@ -5,11 +5,13 @@
 
 from mcp import types
 
-from brainlayer.mcp import list_tools, server
+import brainlayer.mcp as mcp_module
+from brainlayer.mcp import _full_tool_definitions, server
+from brainlayer.mcp.palette import ToolPalette
 
 
 def _get_tools():
-    return asyncio.run(list_tools())
+    return _full_tool_definitions()
 
 
 def _iter_string_fields(schema: dict[str, Any], path: str = ""):
@@ -61,7 +63,8 @@ async def _call_brain_digest(arguments: dict[str, Any]):
     return await handler(request)
 
 
-def test_brain_digest_schema_rejects_oversized_content():
+def test_brain_digest_schema_rejects_oversized_content(monkeypatch):
+    monkeypatch.setattr(mcp_module, "_tool_palette", ToolPalette("full"))
     result = asyncio.run(_call_brain_digest({"content": "x" * 200_001})).root
 
     assert result.isError is True
diff --git a/tests/test_mcp_palette.py b/tests/test_mcp_palette.py
new file mode 100644
index 00000000..543af736
--- /dev/null
+++ b/tests/test_mcp_palette.py
@@ -0,0 +1,66 @@
+"""Tests for the stateful BrainLayer MCP tool palette."""
+
+import asyncio
+
+import pytest
+
+import brainlayer.mcp as mcp_module
+from brainlayer.mcp import _full_tool_definitions, call_tool, list_tools
+from brainlayer.mcp.palette import CORE_TOOL_NAMES, ToolPalette
+
+CORE_WITH_CONTROL = (*CORE_TOOL_NAMES, "expand_palette")
+
+
+@pytest.mark.parametrize("profile", [None, "", "   ", "core", "bogus"])
+def test_core_profiles_fail_closed(monkeypatch, profile):
+    monkeypatch.delenv("BRAINLAYER_MCP_PROFILE", raising=False)
+    palette = ToolPalette(profile)
+
+    assert tuple(tool.name for tool in palette.expose(_full_tool_definitions())) == CORE_WITH_CONTROL
+
+
+@pytest.mark.parametrize("profile", ["full", "operator"])
+def test_full_profiles_preserve_all_python_tools(profile):
+    tools = ToolPalette(profile).expose(_full_tool_definitions())
+
+    assert len(tools) == 13
+    assert tuple(tool.name for tool in tools) == tuple(tool.name for tool in _full_tool_definitions())
+
+
+def test_environment_profile_is_resolved_once(monkeypatch):
+    monkeypatch.setenv("BRAINLAYER_MCP_PROFILE", "operator")
+    palette = ToolPalette()
+    monkeypatch.setenv("BRAINLAYER_MCP_PROFILE", "core")
+
+    assert len(palette.expose(_full_tool_definitions())) == 13
+
+
+def test_python_palette_expands_once_and_dispatches_deferred_tools(monkeypatch):
+    palette = ToolPalette("core")
+    monkeypatch.setattr(mcp_module, "_tool_palette", palette)
+
+    assert tuple(tool.name for tool in asyncio.run(list_tools())) == CORE_WITH_CONTROL
+
+    before = asyncio.run(call_tool("brain_tags", {}))
+    assert before.isError is True
+    assert "not exposed" in before.content[0].text
+
+    first = asyncio.run(call_tool("expand_palette", {}))
+    assert first.isError is False
+    assert first.structuredContent == {
+        "expanded": True,
+        "already_expanded": False,
+        "registered_tools": [tool.name for tool in _full_tool_definitions() if tool.name not in CORE_TOOL_NAMES],
+    }
+    assert len(asyncio.run(list_tools())) == 13
+
+    after = asyncio.run(call_tool("brain_tags", {}))
+    assert "deprecated" in after.content[0].text
+
+    second = asyncio.run(call_tool("expand_palette", {}))
+    assert second.structuredContent == {
+        "expanded": False,
+        "already_expanded": True,
+        "registered_tools": [],
+    }
+    assert len(asyncio.run(list_tools())) == 13
diff --git a/tests/test_measure_mcp_palette.py b/tests/test_measure_mcp_palette.py
new file mode 100644
index 00000000..3fbe4a70
--- /dev/null
+++ b/tests/test_measure_mcp_palette.py
@@ -0,0 +1,42 @@
+"""Tests for deterministic MCP palette measurement."""
+
+import json
+
+import tiktoken
+
+from scripts.measure_mcp_palette import extract_tools, main, measure_tools
+
+
+def test_measure_tools_uses_compact_utf8_json_and_o200k_tokens():
+    tools = [
+        {
+            "name": "memory_זיכרון",
+            "inputSchema": {"properties": {}, "type": "object"},
+        }
+    ]
+    canonical = json.dumps(tools, ensure_ascii=False, separators=(",", ":"), sort_keys=True)
+
+    measurement = measure_tools(tools)
+
+    assert measurement == {
+        "tools": 1,
+        "bytes": len(canonical.encode("utf-8")),
+        "tokens": len(tiktoken.get_encoding("o200k_base").encode(canonical)),
+    }
+
+
+def test_extract_tools_accepts_jsonrpc_envelope():
+    tools = [{"name": "brain_search", "inputSchema": {"type": "object"}}]
+
+    assert extract_tools({"jsonrpc": "2.0", "id": 1, "result": {"tools": tools}}) == tools
+
+
+def test_main_enforces_max_bytes(tmp_path, capsys):
+    payload_path = tmp_path / "tools.json"
+    payload_path.write_text(json.dumps({"tools": [{"name": "brain_search"}]}), encoding="utf-8")
+
+    assert main([str(payload_path), "--max-bytes", "1"]) == 1
+    output = json.loads(capsys.readouterr().out)
+    assert output["bytes"] > 1
+
+    assert main([str(payload_path), "--max-bytes", str(output["bytes"])]) == 0
diff --git a/tests/test_phase3_digest.py b/tests/test_phase3_digest.py
index b7f36c90..1924bcdd 100644
--- a/tests/test_phase3_digest.py
+++ b/tests/test_phase3_digest.py
@@ -287,23 +287,20 @@ def fake_faceted_enrich(*, content, project, title, participants):  # noqa: ARG0
 
 
 def test_brain_digest_tool_exists():
-    """brain_digest tool is registered in MCP server."""
-    import asyncio
+    """brain_digest tool is registered in the full MCP profile."""
 
-    from brainlayer.mcp import list_tools
+    from brainlayer.mcp import _full_tool_definitions
 
-    tools = asyncio.run(list_tools())
+    tools = _full_tool_definitions()
     tool_names = [t.name for t in tools]
     assert "brain_digest" in tool_names
 
 
 def test_brain_digest_schema_has_required_fields():
     """brain_digest tool exposes digest fields and mode-based enrich controls."""
-    import asyncio
+    from brainlayer.mcp import _full_tool_definitions
 
-    from brainlayer.mcp import list_tools
-
-    tools = asyncio.run(list_tools())
+    tools = _full_tool_definitions()
     digest = next(t for t in tools if t.name == "brain_digest")
     props = digest.inputSchema.get("properties", {})
     assert "content" in props
@@ -315,11 +312,9 @@ def test_brain_digest_schema_has_required_fields():
 
 def test_brain_digest_description_teaches_routing():
     """brain_digest description explains when to use it and how it differs from brain_store."""
-    import asyncio
+    from brainlayer.mcp import _full_tool_definitions
 
-    from brainlayer.mcp import list_tools
-
-    tools = asyncio.run(list_tools())
+    tools = _full_tool_definitions()
     digest = next(t for t in tools if t.name == "brain_digest")
     desc = digest.description.lower()
 
@@ -336,23 +331,20 @@ def test_brain_digest_description_teaches_routing():
 
 
 def test_brain_entity_tool_exists():
-    """brain_entity tool is registered in MCP server."""
-    import asyncio
+    """brain_entity tool is registered in the full MCP profile."""
 
-    from brainlayer.mcp import list_tools
+    from brainlayer.mcp import _full_tool_definitions
 
-    tools = asyncio.run(list_tools())
+    tools = _full_tool_definitions()
     tool_names = [t.name for t in tools]
     assert "brain_entity" in tool_names
 
 
 def test_brain_entity_schema():
     """brain_entity keeps query in properties even when optional."""
-    import asyncio
-
-    from brainlayer.mcp import list_tools
+    from brainlayer.mcp import _full_tool_definitions
 
-    tools = asyncio.run(list_tools())
+    tools = _full_tool_definitions()
     entity_tool = next(t for t in tools if t.name == "brain_entity")
     props = entity_tool.inputSchema.get("properties", {})
     assert "query" in props
diff --git a/tests/test_search_filter_params.py b/tests/test_search_filter_params.py
index 74d95c70..721c3647 100644
--- a/tests/test_search_filter_params.py
+++ b/tests/test_search_filter_params.py
@@ -803,9 +803,9 @@ class TestBrainResumeSchema:
     """Verify the explicit checkpoint resume tool is exposed."""
 
     def test_brain_resume_tool_schema(self):
-        from brainlayer.mcp import list_tools
+        from brainlayer.mcp import _full_tool_definitions
 
-        tools = asyncio.run(list_tools())
+        tools = _full_tool_definitions()
         brain_resume = next(tool for tool in tools if tool.name == "brain_resume")
         props = brain_resume.inputSchema["properties"]
 
diff --git a/tests/test_think_recall_integration.py b/tests/test_think_recall_integration.py
index 038e8785..a02d7897 100644
--- a/tests/test_think_recall_integration.py
+++ b/tests/test_think_recall_integration.py
@@ -246,12 +246,11 @@ class TestMCPToolCount:
     """Verify MCP server has correct tool count."""
 
     def test_tool_count(self):
-        """MCP server should have 13 tools including explicit checkpoint resume."""
-        import asyncio
+        """Full MCP profile has 13 tools including explicit checkpoint resume."""
 
-        from brainlayer.mcp import list_tools
+        from brainlayer.mcp import _full_tool_definitions
 
-        tools = asyncio.run(list_tools())
+        tools = _full_tool_definitions()
         assert len(tools) == 13
 
     def test_consolidated_tools_registered(self):
diff --git a/tests/test_tool_annotations.py b/tests/test_tool_annotations.py
index e192fc66..4f0d9960 100644
--- a/tests/test_tool_annotations.py
+++ b/tests/test_tool_annotations.py
@@ -67,9 +67,9 @@ class TestToolAnnotationsPresent:
     """Every tool MUST have ToolAnnotations with readOnlyHint, destructiveHint, idempotentHint."""
 
     def _get_tools(self):
-        from brainlayer.mcp import list_tools
+        from brainlayer.mcp import _full_tool_definitions
 
-        return asyncio.run(list_tools())
+        return _full_tool_definitions()
 
     def test_all_tools_have_annotations(self):
         """Every expected tool must have a non-None annotations field."""
diff --git a/tests/test_tool_description_quality.py b/tests/test_tool_description_quality.py
index 83cfc21b..8fec35e0 100644
--- a/tests/test_tool_description_quality.py
+++ b/tests/test_tool_description_quality.py
@@ -1,6 +1,4 @@
-import asyncio
-
-from brainlayer.mcp import list_tools
+from brainlayer.mcp import _full_tool_definitions
 
 ACTIVE_TOOL_NAMES = {
     "brain_search",
@@ -13,7 +11,7 @@
 
 
 def _tool_descriptions() -> dict[str, str]:
-    tools = asyncio.run(list_tools())
+    tools = _full_tool_definitions()
     return {tool.name: tool.description for tool in tools}