diff --git a/packages/core/src/handlers/ack.ts b/packages/core/src/handlers/ack.ts
new file mode 100644
index 0000000..8a1bc51
--- /dev/null
+++ b/packages/core/src/handlers/ack.ts
@@ -0,0 +1,201 @@
+/**
+ * Handler for acknowledging feedback comments.
+ *
+ * Acknowledges one or more comments locally and optionally adds a thumbs-up
+ * reaction on GitHub. Supports undo via the undo flag.
+ */
+
+import { NotFoundError, Result } from "@outfitter/contracts";
+
+import { detectAuth } from "../auth";
+import { type AckRecord, addAcks, isAcked, removeAck } from "../ack";
+import {
+  batchAddReactions,
+  deduplicateByCommentId,
+  partitionResolutions,
+  resolveBatchIds,
+} from "../batch";
+import { formatDisplayId } from "../render/ids";
+import { classifyId, generateShortId } from "../short-id";
+import type { HandlerContext } from "./types";
+
+// =============================================================================
+// Types
+// =============================================================================
+
+/** Input parameters for the ack handler. */
+export interface AckInput {
+  /** IDs to acknowledge — short IDs, comment IDs, or PR numbers */
+  ids: string[];
+  /** Repository (owner/repo) */
+  repo: string;
+  /** Add thumbs-up reaction on GitHub */
+  react?: boolean | undefined;
+  /** Undo a previous ack */
+  undo?: boolean | undefined;
+}
+
+/** Per-ID result for ack operations. */
+export interface AckItemResult {
+  /** Short display ID */
+  id: string;
+  /** Whether this operation succeeded */
+  ok: boolean;
+  /** Error message if not ok */
+  error?: string | undefined;
+}
+
+/** Structured output from the ack handler. */
+export interface AckOutput {
+  /** Number of entries acknowledged (or un-acknowledged) */
+  acked: number;
+  /** Number of reactions added */
+  reactionsAdded: number;
+  /** Individual results per ID */
+  results: AckItemResult[];
+}
+
+// =============================================================================
+// Handler
+// =============================================================================
+
+/**
+ * Acknowledge feedback comments, optionally adding GitHub reactions.
+ *
+ * Resolves each ID from the cache, checks ack status, and records acks locally.
+ * When react=true, attempts to add a thumbs-up reaction (requires auth).
+ * When undo=true, removes existing acks instead.
+ *
+ * @param input - Ack input including IDs, repo, and options
+ * @param ctx - Handler context with config, db, and logger
+ * @returns Result containing AckOutput on success
+ */
+export async function ackHandler(
+  input: AckInput,
+  ctx: HandlerContext
+): Promise<Result<AckOutput, Error>> {
+  if (input.ids.length === 0) {
+    return Result.err(
+      new NotFoundError({
+        message: "At least one ID is required.",
+        resourceType: "comment",
+        resourceId: "",
+      })
+    );
+  }
+
+  // Filter out PR numbers (not supported in ack)
+  const commentIds = input.ids.filter((id) => classifyId(id) !== "pr_number");
+  if (commentIds.length === 0) {
+    return Result.err(
+      new NotFoundError({
+        message: "No comment IDs provided. Use PR numbers with a dedicated bulk ack command.",
+        resourceType: "comment",
+        resourceId: input.ids[0] ?? "",
+      })
+    );
+  }
+
+  // Resolve all comment IDs in a single batch
+  const resolutions = await resolveBatchIds(commentIds, input.repo);
+  const { comments, errors } = partitionResolutions(resolutions);
+  const uniqueComments = deduplicateByCommentId(comments);
+
+  const itemResults: AckItemResult[] = [];
+
+  // Collect error results
+  for (const e of errors) {
+    itemResults.push({
+      id: e.id,
+      ok: false,
+      error: e.error ?? "Unknown error",
+    });
+  }
+
+  if (uniqueComments.length === 0) {
+    return Result.ok({
+      acked: 0,
+      reactionsAdded: 0,
+      results: itemResults,
+    });
+  }
+
+  // Handle undo: remove acks
+  if (input.undo) {
+    let removed = 0;
+    for (const comment of uniqueComments) {
+      const count = await removeAck(comment.id, input.repo);
+      const shortId = comment.shortId ?? formatDisplayId(generateShortId(comment.id, input.repo));
+      if (count > 0) {
+        removed++;
+        itemResults.push({ id: shortId, ok: true });
+      } else {
+        itemResults.push({ id: shortId, ok: false, error: "Not previously acknowledged." });
+      }
+    }
+    return Result.ok({ acked: removed, reactionsAdded: 0, results: itemResults });
+  }
+
+  // Setup GitHub client for reactions if requested
+  let client = null;
+  if (input.react) {
+    const authResult = await detectAuth(ctx.config.github_token);
+    if (authResult.isOk()) {
+      const { GitHubClient } = await import("../github");
+      client = new GitHubClient(authResult.value.token);
+    } else {
+      ctx.logger.debug("No auth for reactions; acknowledging locally only.");
+    }
+  }
+
+  // Check which are already acked
+  const ackChecks = await Promise.all(
+    uniqueComments.map(async (r) => {
+      const alreadyAcked = await isAcked(r.id, input.repo);
+      return { ...r, alreadyAcked };
+    })
+  );
+
+  const toAck = ackChecks.filter((r) => !r.alreadyAcked);
+  const alreadyAcked = ackChecks.filter((r) => r.alreadyAcked);
+
+  // Add reactions in parallel for newly acked items
+  const reactionResults =
+    client && toAck.length > 0
+      ? await batchAddReactions(toAck.map((r) => r.id), client)
+      : toAck.map((r) => ({ commentId: r.id, reactionAdded: false }));
+
+  const reactionMap = new Map(reactionResults.map((r) => [r.commentId, r.reactionAdded]));
+
+  // Build and store ack records
+  const ackRecords: AckRecord[] = toAck.map((r) => ({
+    repo: input.repo,
+    pr: r.entry?.pr ?? 0,
+    comment_id: r.id,
+    acked_at: new Date().toISOString(),
+    ...(ctx.config.user?.github_username && { acked_by: ctx.config.user.github_username }),
+    reaction_added: reactionMap.get(r.id) ?? false,
+  }));
+
+  if (ackRecords.length > 0) {
+    await addAcks(ackRecords);
+  }
+
+  const reactionsAdded = reactionResults.filter((r) => r.reactionAdded).length;
+
+  // Build per-ID results
+  for (const r of toAck) {
+    const shortId = r.shortId ?? formatDisplayId(generateShortId(r.id, input.repo));
+    itemResults.push({ id: shortId, ok: true });
+  }
+  for (const r of alreadyAcked) {
+    const shortId = r.shortId ?? formatDisplayId(generateShortId(r.id, input.repo));
+    itemResults.push({ id: shortId, ok: true });
+  }
+
+  return Result.ok({
+    acked: toAck.length,
+    reactionsAdded,
+    results: itemResults,
+  });
+}
diff --git a/packages/core/src/handlers/close.ts b/packages/core/src/handlers/close.ts
new file mode 100644
index 0000000..926bacc
--- /dev/null
+++ b/packages/core/src/handlers/close.ts
@@ -0,0 +1,165 @@
+/**
+ * Handler for closing feedback: resolving review threads or closing PRs.
+ *
+ * Polymorphic: accepts a comment ID (resolves the thread) or a PR number
+ * (closes the PR via GitHub API). Returns structured output for formatting.
+ */
+
+import { AuthError, NotFoundError, Result } from "@outfitter/contracts";
+
+import { detectAuth } from "../auth";
+import { queryEntries } from "../query";
+import { formatDisplayId } from "../render/ids";
+import {
+  buildShortIdCache,
+  classifyId,
+  resolveShortId,
+} from "../short-id";
+import type { HandlerContext } from "./types";
+
+// =============================================================================
+// Types
+// =============================================================================
+
+/** Input parameters for the close handler. */
+export interface CloseInput {
+  /** ID to close — short ID, comment ID, or PR number */
+  id: string;
+  /** Repository (owner/repo) */
+  repo: string;
+  /** Comment body when closing (optional) */
+  body?: string | undefined;
+}
+
+/** Structured output from the close handler. */
+export interface CloseOutput {
+  /** What was closed */
+  type: "thread" | "pr";
+  /** Whether it was successfully closed */
+  ok: boolean;
+  /** URL of the closed item */
+  url?: string | undefined;
+}
+
+// =============================================================================
+// Handler
+// =============================================================================
+
+/**
+ * Close a review thread or PR.
+ *
+ * When the ID is a PR number, closes the PR via GitHub API.
+ * When the ID is a comment ID (short or full), resolves the review thread
+ * (or acks if it's an issue comment which cannot be resolved).
+ *
+ * @param input - Close input including ID and repo
+ * @param ctx - Handler context with config, db, and logger
+ * @returns Result containing CloseOutput on success
+ */
+export async function closeHandler(
+  input: CloseInput,
+  ctx: HandlerContext
+): Promise<Result<CloseOutput, Error>> {
+  const authResult = await detectAuth(ctx.config.github_token);
+  if (authResult.isErr()) {
+    return Result.err(
+      new AuthError({ message: `Authentication required to close: ${authResult.error.message}` })
+    );
+  }
+
+  const { GitHubClient } = await import("../github");
+  const client = new GitHubClient(authResult.value.token);
+
+  const repoParts = input.repo.split("/");
+  const owner = repoParts[0] ?? "";
+  const name = repoParts[1] ?? "";
+
+  const idType = classifyId(input.id);
+
+  // PR number: close the PR
+  if (idType === "pr_number") {
+    const prNum = Number.parseInt(input.id, 10);
+    const prIdResult = await client.fetchPullRequestId(owner, name, prNum);
+    if (prIdResult.isErr()) {
+      return Result.err(
+        new NotFoundError({
+          message: `PR #${prNum} not found in ${input.repo}.`,
+          resourceType: "pull_request",
+          resourceId: String(prNum),
+        })
+      );
+    }
+
+    const closeResult = await client.closePullRequest(prIdResult.value);
+    if (closeResult.isErr()) {
+      return Result.err(closeResult.error);
+    }
+
+    ctx.logger.debug("PR closed", { pr: prNum, repo: input.repo });
+    return Result.ok({ type: "pr", ok: true });
+  }
+
+  // Comment ID: resolve the review thread
+  const entries = await queryEntries({ filters: { repo: input.repo } });
+  buildShortIdCache(entries);
+
+  let commentId = input.id;
+  if (idType === "short_id") {
+    const mapping = resolveShortId(input.id);
+    if (!mapping) {
+      return Result.err(
+        new NotFoundError({
+          message: `Short ID ${formatDisplayId(input.id)} not found in cache.`,
+          resourceType: "comment",
+          resourceId: input.id,
+        })
+      );
+    }
+    commentId = mapping.fullId;
+  }
+
+  const entry = entries.find((e) => e.id === commentId);
+  if (!entry) {
+    return Result.err(
+      new NotFoundError({
+        message: `Comment ${input.id} not found in cache.`,
+        resourceType: "comment",
+        resourceId: input.id,
+      })
+    );
+  }
+
+  if (entry.subtype !== "review_comment") {
+    // Issue comments cannot be resolved — acknowledge with reaction instead
+    const reactionResult = await client.addReaction(commentId, "THUMBS_UP");
+    if (reactionResult.isErr()) {
+      ctx.logger.debug("Reaction already exists or failed", { commentId });
+    }
+    return Result.ok({ type: "thread", ok: true });
+  }
+
+  // Review comment: find and resolve the thread
+  const threadMapResult = await client.fetchReviewThreadMap(owner, name, entry.pr);
+  if (threadMapResult.isErr()) {
+    return Result.err(threadMapResult.error);
+  }
+
+  const threadId = threadMapResult.value.get(commentId);
+  if (!threadId) {
+    return Result.err(
+      new NotFoundError({
+        message: `No review thread found for comment ${input.id}.`,
+        resourceType: "thread",
+        resourceId: commentId,
+      })
+    );
+  }
+
+  const resolveResult = await client.resolveReviewThread(threadId);
+  if (resolveResult.isErr()) {
+    return Result.err(resolveResult.error);
+  }
+
+  ctx.logger.debug("Thread resolved", { threadId, repo: input.repo });
+  return Result.ok({ type: "thread", ok: true });
+}
diff --git a/packages/core/src/handlers/comment.ts b/packages/core/src/handlers/comment.ts
new file mode 100644
index 0000000..5a6d582
--- /dev/null
+++ b/packages/core/src/handlers/comment.ts
@@ -0,0 +1,91 @@
+/**
+ * Handler for adding a PR-level comment.
+ *
+ * Resolves the PR node ID and posts a new issue comment on the PR.
+ * Returns structured output for CLI/MCP formatting.
+ */
+
+import { AuthError, NotFoundError, Result } from "@outfitter/contracts";
+
+import { detectAuth } from "../auth";
+import type { HandlerContext } from "./types";
+
+// =============================================================================
+// Types
+// =============================================================================
+
+/** Input parameters for the comment handler. */
+export interface CommentInput {
+  /** PR number */
+  pr: number;
+  /** Comment body text */
+  body: string;
+  /** Repository (owner/repo) */
+  repo: string;
+}
+
+/** Structured output from the comment handler. */
+export interface CommentOutput {
+  /** The created comment's node ID */
+  id: string;
+  /** URL to the comment */
+  url?: string | undefined;
+}
+
+// =============================================================================
+// Handler
+// =============================================================================
+
+/**
+ * Add a PR-level comment.
+ *
+ * Resolves the PR node ID via GitHub API and posts a new issue comment.
+ * Returns structured metadata about the created comment.
+ *
+ * @param input - Comment input including PR number, body, and repo
+ * @param ctx - Handler context with config, db, and logger
+ * @returns Result containing CommentOutput on success
+ */
+export async function commentHandler(
+  input: CommentInput,
+  ctx: HandlerContext
+): Promise<Result<CommentOutput, Error>> {
+  const authResult = await detectAuth(ctx.config.github_token);
+  if (authResult.isErr()) {
+    return Result.err(
+      new AuthError({ message: `Authentication required to comment: ${authResult.error.message}` })
+    );
+  }
+
+  const { GitHubClient } = await import("../github");
+  const client = new GitHubClient(authResult.value.token);
+
+  const repoParts = input.repo.split("/");
+  const owner = repoParts[0] ?? "";
+  const name = repoParts[1] ?? "";
+
+  const prIdResult = await client.fetchPullRequestId(owner, name, input.pr);
+  if (prIdResult.isErr()) {
+    return Result.err(
+      new NotFoundError({
+        message: `PR #${input.pr} not found in ${input.repo}.`,
+        resourceType: "pull_request",
+        resourceId: String(input.pr),
+      })
+    );
+  }
+
+  const commentResult = await client.addIssueComment(prIdResult.value, input.body);
+  if (commentResult.isErr()) {
+    return Result.err(commentResult.error);
+  }
+
+  const comment = commentResult.value;
+
+  ctx.logger.debug("Comment added", { pr: input.pr, repo: input.repo, id: comment.id });
+
+  return Result.ok({
+    id: comment.id,
+    ...(comment.url && { url: comment.url }),
+  });
+}
diff --git a/packages/core/src/handlers/index.ts b/packages/core/src/handlers/index.ts
index 0a3f524..7cc83d9 100644
--- a/packages/core/src/handlers/index.ts
+++ b/packages/core/src/handlers/index.ts
@@ -1,3 +1,19 @@
+export {
+  ackHandler,
+  type AckInput,
+  type AckItemResult,
+  type AckOutput,
+} from "./ack";
+export {
+  closeHandler,
+  type CloseInput,
+  type CloseOutput,
+} from "./close";
+export {
+  commentHandler,
+  type CommentInput,
+  type CommentOutput,
+} from "./comment";
 export {
   doctorHandler,
   type DoctorCheckResult,
@@ -9,6 +25,11 @@ export {
   type QueryInput,
   type QueryOutput,
 } from "./query";
+export {
+  replyHandler,
+  type ReplyInput,
+  type ReplyOutput,
+} from "./reply";
 export {
   getCacheStats,
   statusHandler,
diff --git a/packages/core/src/handlers/reply.ts b/packages/core/src/handlers/reply.ts
new file mode 100644
index 0000000..4a37b41
--- /dev/null
+++ b/packages/core/src/handlers/reply.ts
@@ -0,0 +1,161 @@
+/**
+ * Handler for replying to a review thread comment.
+ *
+ * Resolves the target ID, finds the thread, posts a reply, and optionally
+ * resolves the thread. Returns structured output for CLI/MCP formatting.
+ */
+
+import { AuthError, NotFoundError, Result } from "@outfitter/contracts";
+
+import { detectAuth } from "../auth";
+import { queryEntries } from "../query";
+import { formatDisplayId } from "../render/ids";
+import {
+  buildShortIdCache,
+  classifyId,
+  generateShortId,
+  resolveShortId,
+} from "../short-id";
+import type { HandlerContext } from "./types";
+
+// =============================================================================
+// Types
+// =============================================================================
+
+/** Input parameters for the reply handler. */
+export interface ReplyInput {
+  /** Thread ID to reply to — short ID (@abc), comment ID, or PR number */
+  id: string;
+  /** Reply body text */
+  body: string;
+  /** Repository (owner/repo) */
+  repo: string;
+  /** Optionally resolve the thread after replying */
+  resolve?: boolean | undefined;
+}
+
+/** Structured output from the reply handler. */
+export interface ReplyOutput {
+  /** The created reply's node ID */
+  id: string;
+  /** URL to the reply */
+  url?: string | undefined;
+  /** Whether the thread was resolved */
+  resolved?: boolean | undefined;
+}
+
+// =============================================================================
+// Handler
+// =============================================================================
+
+/**
+ * Reply to a review thread comment.
+ *
+ * Resolves the ID (short → full), locates the review thread, posts the reply,
+ * and optionally resolves the thread. Returns a Result with reply metadata.
+ *
+ * @param input - Reply input including target ID, body, and repo
+ * @param ctx - Handler context with config, db, and logger
+ * @returns Result containing ReplyOutput on success
+ */
+export async function replyHandler(
+  input: ReplyInput,
+  ctx: HandlerContext
+): Promise<Result<ReplyOutput, Error>> {
+  const authResult = await detectAuth(ctx.config.github_token);
+  if (authResult.isErr()) {
+    return Result.err(
+      new AuthError({ message: `Authentication required to reply: ${authResult.error.message}` })
+    );
+  }
+
+  const { GitHubClient } = await import("../github");
+  const client = new GitHubClient(authResult.value.token);
+
+  const idType = classifyId(input.id);
+
+  if (idType === "pr_number") {
+    return Result.err(
+      new NotFoundError({
+        message: "Use commentHandler to comment on a PR by number. replyHandler expects a comment ID.",
+        resourceType: "comment",
+        resourceId: input.id,
+      })
+    );
+  }
+
+  // Load entries to resolve short ID
+  const entries = await queryEntries({ filters: { repo: input.repo } });
+  buildShortIdCache(entries);
+
+  let commentId = input.id;
+  if (idType === "short_id") {
+    const mapping = resolveShortId(input.id);
+    if (!mapping) {
+      return Result.err(
+        new NotFoundError({
+          message: `Short ID ${formatDisplayId(input.id)} not found in cache.`,
+          resourceType: "comment",
+          resourceId: input.id,
+        })
+      );
+    }
+    commentId = mapping.fullId;
+  }
+
+  const entry = entries.find((e) => e.id === commentId);
+  if (!entry) {
+    return Result.err(
+      new NotFoundError({
+        message: `Comment ${input.id} not found in cache.`,
+        resourceType: "comment",
+        resourceId: input.id,
+      })
+    );
+  }
+
+  const repoParts = input.repo.split("/");
+  const owner = repoParts[0] ?? "";
+  const name = repoParts[1] ?? "";
+
+  const threadMapResult = await client.fetchReviewThreadMap(owner, name, entry.pr);
+  if (threadMapResult.isErr()) {
+    return Result.err(threadMapResult.error);
+  }
+
+  const threadId = threadMapResult.value.get(commentId);
+  if (!threadId) {
+    return Result.err(
+      new NotFoundError({
+        message: `No review thread found for comment ${input.id}.`,
+        resourceType: "thread",
+        resourceId: commentId,
+      })
+    );
+  }
+
+  const replyResult = await client.addReviewThreadReply(threadId, input.body);
+  if (replyResult.isErr()) {
+    return Result.err(replyResult.error);
+  }
+
+  const reply = replyResult.value;
+
+  const shortId = formatDisplayId(generateShortId(reply.id, input.repo));
+
+  if (input.resolve) {
+    const resolveResult = await client.resolveReviewThread(threadId);
+    if (resolveResult.isErr()) {
+      ctx.logger.warn("Failed to resolve thread after reply", {
+        threadId,
+        error: resolveResult.error.message,
+      });
+    }
+  }
+
+  return Result.ok({
+    id: shortId,
+    ...(reply.url && { url: reply.url }),
+    ...(input.resolve && { resolved: true }),
+  });
+}