fix: use readFileState for Edit read-before-edit check, align with Claude Code

[lewis617]

Problem

Edit's read-before-edit check used messageManager.hasFileBeenRead() which only tracked Read tool results. The Write tool only updates context.readFileState, so Write → Edit failed without an intermediate Read — the agent had to Read a file it just wrote.

Fix

Changed Edit's read-before-edit check from messageManager.hasFileBeenRead(filePath) to context.readFileState?.has(resolvedPath).

readFileState is populated by Read, Write, and Edit tools — a single source of truth, matching Claude Code's readFileState approach where all three tools write to the same Map.

Changes

• packages/agent-sdk/src/tools/editTool.ts: Moved resolvedPath computation before the check; replaced messageManager.hasFileBeenRead() with context.readFileState?.has(resolvedPath)
• packages/agent-sdk/tests/tools/editTool.test.ts:
  • Pre-populated readFileState in beforeEach for happy-path tests
  • Added default stat mock returning matching mtime to prevent staleness check crashes
  • Updated rejection test to use empty readFileState instead of mocking messageManager
  • Updated allow test to use path-specific readFileState
  • Renamed "skip staleness check" test to "reject edit when readFileState is not provided" (now expects failure)

Test Results

• 24/24 editTool tests pass
• 65/65 related tool tests pass (writeTool, readTool, editToolSerialization)
• Build and type-check pass

Notes

messageManager.hasFileBeenRead() and recentFileReads are left intact — still used by getRecentFileReads() for compaction context attachment.