diff --git a/src/auto-reply/reply/agent-runner-memory.dedup.test.ts b/src/auto-reply/reply/agent-runner-memory.dedup.test.ts
new file mode 100644
index 00000000000..d2afa5a3e6f
--- /dev/null
+++ b/src/auto-reply/reply/agent-runner-memory.dedup.test.ts
@@ -0,0 +1,209 @@
+/**
+ * Regression tests for the hash-based memory flush dedup logic (#34222).
+ *
+ * These tests verify that:
+ * - Duplicate MEMORY.md writes are prevented when the transcript hasn't changed
+ * - Compaction events correctly signal completion status via `completed`
+ * - Post-flush hash is stored correctly for subsequent dedup checks
+ * - Session reset clears hash, allowing the first flush after reset
+ */
+import crypto from "node:crypto";
+import { describe, expect, it } from "vitest";
+
+// Inline computeContextHash to avoid importing memory-flush.js (which
+// triggers the full agent import chain and hits the missing pi-ai/oauth
+// package in test environments).  This mirrors the implementation in
+// src/auto-reply/reply/memory-flush.ts exactly.
+function computeContextHash(messages: Array<{ role?: string; content?: unknown }>): string {
+  const userAssistant = messages.filter((m) => m.role === "user" || m.role === "assistant");
+  const tail = userAssistant.slice(-3);
+  const payload = `${messages.length}:${tail.map((m, i) => `[${i}:${m.role ?? ""}]${typeof m.content === "string" ? m.content : JSON.stringify(m.content ?? "")}`).join("\x00")}`;
+  const hash = crypto.createHash("sha256").update(payload).digest("hex");
+  return hash.slice(0, 16);
+}
+
+function shouldSkipFlushByHash(
+  tailMessages: Array<{ role?: string; content?: unknown }>,
+  previousHash: string | undefined,
+): { skip: boolean; hash: string | undefined } {
+  if (tailMessages.length === 0) {
+    return { skip: false, hash: undefined };
+  }
+  const hash = computeContextHash(tailMessages);
+  if (previousHash && hash === previousHash) {
+    return { skip: true, hash };
+  }
+  return { skip: false, hash };
+}
+
+function shouldMarkCompactionCompleted(eventData: {
+  phase?: string;
+  completed?: boolean;
+  willRetry?: boolean;
+}): boolean {
+  const phase = typeof eventData.phase === "string" ? eventData.phase : "";
+  return phase === "end" && eventData.completed === true;
+}
+
+describe("hash-based memory flush dedup", () => {
+  const transcript = [
+    { role: "user", content: "hello world" },
+    { role: "assistant", content: "Hi there! How can I help?" },
+  ];
+
+  it("first flush — no previous hash, should NOT skip", () => {
+    const result = shouldSkipFlushByHash(transcript, undefined);
+    expect(result.skip).toBe(false);
+    expect(result.hash).toBeDefined();
+  });
+
+  it("same transcript — hash matches, should skip", () => {
+    const hash = computeContextHash(transcript);
+    const result = shouldSkipFlushByHash(transcript, hash);
+    expect(result.skip).toBe(true);
+    expect(result.hash).toBe(hash);
+  });
+
+  it("different transcript — hash mismatch, should NOT skip", () => {
+    const previousHash = computeContextHash(transcript);
+    const changedTranscript = [...transcript, { role: "user", content: "tell me more" }];
+    const result = shouldSkipFlushByHash(changedTranscript, previousHash);
+    expect(result.skip).toBe(false);
+    expect(result.hash).not.toBe(previousHash);
+  });
+
+  it("empty transcript tail — should NOT skip (degenerate case)", () => {
+    const result = shouldSkipFlushByHash([], "somehash");
+    expect(result.skip).toBe(false);
+    expect(result.hash).toBeUndefined();
+  });
+
+  it("session reset clears hash — first flush after reset should NOT skip", () => {
+    const clearedHash: string | undefined = undefined;
+    const result = shouldSkipFlushByHash(transcript, clearedHash);
+    expect(result.skip).toBe(false);
+  });
+});
+
+describe("post-flush hash storage", () => {
+  it("post-flush hash differs from pre-flush hash (flush appends messages)", () => {
+    const preFlushTail = [
+      { role: "user", content: "hello" },
+      { role: "assistant", content: "hi" },
+    ];
+    const postFlushTail = [
+      ...preFlushTail,
+      { role: "user", content: "Write a memory summary" },
+      { role: "assistant", content: "Memory updated for 2026-03-13" },
+    ];
+
+    const preHash = computeContextHash(preFlushTail);
+    const postHash = computeContextHash(postFlushTail);
+    expect(preHash).not.toBe(postHash);
+  });
+
+  it("next dedup check matches stored post-flush hash when transcript unchanged", () => {
+    const postFlushTail = [
+      { role: "user", content: "hello" },
+      { role: "assistant", content: "hi" },
+      { role: "user", content: "Write a memory summary" },
+      { role: "assistant", content: "Memory updated" },
+    ];
+    const storedHash = computeContextHash(postFlushTail);
+    const nextCheckResult = shouldSkipFlushByHash(postFlushTail, storedHash);
+    expect(nextCheckResult.skip).toBe(true);
+  });
+
+  it("next dedup check does NOT match after new user messages arrive", () => {
+    const postFlushTail = [
+      { role: "user", content: "hello" },
+      { role: "assistant", content: "Memory updated" },
+    ];
+    const storedHash = computeContextHash(postFlushTail);
+    const newTail = [
+      ...postFlushTail,
+      { role: "user", content: "What about tomorrow?" },
+      { role: "assistant", content: "Let me check the calendar" },
+    ];
+    const nextCheckResult = shouldSkipFlushByHash(newTail, storedHash);
+    expect(nextCheckResult.skip).toBe(false);
+  });
+});
+
+describe("compaction event completion detection", () => {
+  it("successful compaction (completed=true) → completed", () => {
+    expect(
+      shouldMarkCompactionCompleted({
+        phase: "end",
+        completed: true,
+        willRetry: false,
+      }),
+    ).toBe(true);
+  });
+
+  it("willRetry=true with completed=true → still completed (overflow recovery)", () => {
+    expect(
+      shouldMarkCompactionCompleted({
+        phase: "end",
+        completed: true,
+        willRetry: true,
+      }),
+    ).toBe(true);
+  });
+
+  it("aborted compaction (completed=false) → NOT completed", () => {
+    expect(
+      shouldMarkCompactionCompleted({
+        phase: "end",
+        completed: false,
+        willRetry: false,
+      }),
+    ).toBe(false);
+  });
+
+  it("missing completed field → NOT completed (strict check)", () => {
+    expect(
+      shouldMarkCompactionCompleted({
+        phase: "end",
+        willRetry: false,
+      }),
+    ).toBe(false);
+  });
+
+  it("start phase → NOT completed", () => {
+    expect(
+      shouldMarkCompactionCompleted({
+        phase: "start",
+        completed: true,
+      }),
+    ).toBe(false);
+  });
+});
+
+// ---------------------------------------------------------------------------
+// Pending prompt inclusion in hash
+// ---------------------------------------------------------------------------
+
+describe("pending prompt inclusion in hash", () => {
+  it("hash differs when pending prompt is included vs excluded", () => {
+    const transcript = [
+      { role: "user", content: "hello" },
+      { role: "assistant", content: "Memory updated" },
+    ];
+    const hashWithout = computeContextHash(transcript);
+    const withPrompt = [...transcript, { role: "user", content: "new question" }];
+    const hashWith = computeContextHash(withPrompt);
+    expect(hashWith).not.toBe(hashWithout);
+  });
+
+  it("same transcript + same prompt = same hash (dedup works)", () => {
+    const transcript = [
+      { role: "user", content: "hello" },
+      { role: "assistant", content: "Memory updated" },
+      { role: "user", content: "same prompt" },
+    ];
+    const hash1 = computeContextHash(transcript);
+    const hash2 = computeContextHash(transcript);
+    expect(hash1).toBe(hash2);
+  });
+});
diff --git a/src/auto-reply/reply/agent-runner-memory.ts b/src/auto-reply/reply/agent-runner-memory.ts
index 267326a7e20..c6b36eb0029 100644
--- a/src/auto-reply/reply/agent-runner-memory.ts
+++ b/src/auto-reply/reply/agent-runner-memory.ts
@@ -37,6 +37,7 @@ import {
   resolveMemoryFlushPromptForRun,
   resolveMemoryFlushSettings,
   shouldRunMemoryFlush,
+  computeContextHash,
 } from "./memory-flush.js";
 import type { FollowupRun } from "./queue.js";
 import { incrementCompactionCount } from "./session-updates.js";
@@ -447,6 +448,47 @@ export async function runMemoryFlushIfNeeded(params: {
     return entry ?? params.sessionEntry;
   }
 
+  // --- Content hash dedup (state-based) ---
+  // Read the tail of the session transcript and compute a lightweight hash.
+  // If the hash matches the last flush, the context hasn't materially changed
+  // and flushing again would produce duplicate memory entries (#30115).
+  const sessionFilePath = await resolveSessionFilePathForFlush(
+    params.followupRun.run.sessionId,
+    entry ?? params.sessionEntry,
+    params.storePath,
+    params.sessionKey ? resolveAgentIdFromSessionKey(params.sessionKey) : undefined,
+  );
+  let contextHashBeforeFlush: string | undefined;
+  if (sessionFilePath) {
+    try {
+      const tailMessages = await readTranscriptTailMessages(sessionFilePath, 10);
+      // Include the pending prompt in the hash — runMemoryFlushIfNeeded runs
+      // before the current prompt is appended to the transcript, so the
+      // persisted tail alone would match the post-flush hash and incorrectly
+      // skip the next flush even when a new user message arrived.
+      const currentPrompt = params.followupRun.prompt;
+      if (currentPrompt) {
+        tailMessages.push({ role: "user", content: currentPrompt });
+      }
+      if (tailMessages.length === 0) {
+        logVerbose(
+          `memoryFlush dedup skipped (no tail messages extracted): sessionKey=${params.sessionKey}`,
+        );
+      }
+      contextHashBeforeFlush =
+        tailMessages.length > 0 ? computeContextHash(tailMessages) : undefined;
+      const previousHash = entry?.memoryFlushContextHash;
+      if (previousHash && contextHashBeforeFlush === previousHash) {
+        logVerbose(
+          `memoryFlush skipped (context hash unchanged): sessionKey=${params.sessionKey} hash=${contextHashBeforeFlush}`,
+        );
+        return entry ?? params.sessionEntry;
+      }
+    } catch (err) {
+      logVerbose(`memoryFlush hash check failed, proceeding with flush: ${String(err)}`);
+    }
+  }
+
   logVerbose(
     `memoryFlush triggered: sessionKey=${params.sessionKey} tokenCount=${tokenCountForFlush ?? "undefined"} threshold=${flushThreshold}`,
   );
@@ -509,7 +551,7 @@ export async function runMemoryFlushIfNeeded(params: {
           onAgentEvent: (evt) => {
             if (evt.stream === "compaction") {
               const phase = typeof evt.data.phase === "string" ? evt.data.phase : "";
-              if (phase === "end") {
+              if (phase === "end" && evt.data.completed === true) {
                 memoryCompactionCompleted = true;
               }
             }
@@ -538,12 +580,29 @@ export async function runMemoryFlushIfNeeded(params: {
     }
     if (params.storePath && params.sessionKey) {
       try {
+        // Re-hash the transcript AFTER the flush so the stored hash matches
+        // what the next pre-flush check will compute (the transcript now
+        // includes the flush turn's messages). (#34222)
+        let contextHashAfterFlush = contextHashBeforeFlush;
+        if (sessionFilePath) {
+          try {
+            const postFlushMessages = await readTranscriptTailMessages(sessionFilePath, 10);
+            if (postFlushMessages.length > 0) {
+              contextHashAfterFlush = computeContextHash(postFlushMessages);
+            }
+          } catch {
+            // Best-effort: fall back to pre-flush hash if re-read fails.
+          }
+        }
         const updatedEntry = await updateSessionStoreEntry({
           storePath: params.storePath,
           sessionKey: params.sessionKey,
           update: async () => ({
             memoryFlushAt: Date.now(),
             memoryFlushCompactionCount,
+            // Always write the hash field — when rehashing fails, clearing
+            // the stale value prevents incorrect dedup on subsequent flushes.
+            memoryFlushContextHash: contextHashAfterFlush ?? undefined,
           }),
         });
         if (updatedEntry) {
@@ -559,3 +618,64 @@ export async function runMemoryFlushIfNeeded(params: {
 
   return activeSessionEntry;
 }
+
+/**
+ * Resolve the session transcript file path for flush hash computation.
+ */
+async function resolveSessionFilePathForFlush(
+  sessionId: string | undefined,
+  entry: SessionEntry | undefined,
+  storePath: string | undefined,
+  agentId: string | undefined,
+): Promise<string | undefined> {
+  if (!sessionId) {
+    return undefined;
+  }
+  const resolved = resolveSessionFilePath(
+    sessionId,
+    entry,
+    resolveSessionFilePathOptions({ agentId, storePath }),
+  );
+  return resolved ?? undefined;
+}
+
+/**
+ * Read the last N messages from a session transcript file.
+ * Only reads the tail of the file to avoid loading multi-MB transcripts.
+ */
+async function readTranscriptTailMessages(
+  filePath: string,
+  maxMessages: number,
+): Promise<Array<{ role?: string; content?: unknown }>> {
+  const TAIL_BYTES = 64 * 1024;
+  const handle = await fs.promises.open(filePath, "r");
+  try {
+    const stat = await handle.stat();
+    const start = Math.max(0, stat.size - TAIL_BYTES);
+    const readLen = Math.min(stat.size, TAIL_BYTES);
+    const buf = Buffer.alloc(readLen);
+    await handle.read(buf, 0, readLen, start);
+    const tail = buf.toString("utf-8");
+    const nlIdx = tail.indexOf("\n");
+    const trimmed = start > 0 ? (nlIdx >= 0 ? tail.slice(nlIdx + 1) : "") : tail;
+    const lines = trimmed.split(/\r?\n/);
+    const messages: Array<{ role?: string; content?: unknown }> = [];
+    for (let i = lines.length - 1; i >= 0 && messages.length < maxMessages; i--) {
+      const line = lines[i].trim();
+      if (!line) {
+        continue;
+      }
+      try {
+        const parsed = JSON.parse(line);
+        if (parsed?.message?.role) {
+          messages.unshift({ role: parsed.message.role, content: parsed.message.content });
+        }
+      } catch {
+        // Skip malformed lines
+      }
+    }
+    return messages;
+  } finally {
+    await handle.close();
+  }
+}
diff --git a/src/auto-reply/reply/agent-runner.runreplyagent.e2e.test.ts b/src/auto-reply/reply/agent-runner.runreplyagent.e2e.test.ts
index 6bebdc6a390..ce4d5bae9e5 100644
--- a/src/auto-reply/reply/agent-runner.runreplyagent.e2e.test.ts
+++ b/src/auto-reply/reply/agent-runner.runreplyagent.e2e.test.ts
@@ -716,7 +716,7 @@ describe("runReplyAgent typing (heartbeat)", () => {
       state.runEmbeddedPiAgentMock.mockImplementationOnce(async (params: AgentRunParams) => {
         params.onAgentEvent?.({
           stream: "compaction",
-          data: { phase: "end", willRetry: false },
+          data: { phase: "end", willRetry: false, completed: true },
         });
         return { payloads: [{ text: "final" }], meta: {} };
       });
@@ -2048,7 +2048,7 @@ describe("runReplyAgent memory flush", () => {
         if (params.prompt?.includes("Pre-compaction memory flush.")) {
           params.onAgentEvent?.({
             stream: "compaction",
-            data: { phase: "end", willRetry: false },
+            data: { phase: "end", willRetry: false, completed: true },
           });
           return { payloads: [], meta: {} };
         }
diff --git a/src/auto-reply/reply/agent-runner.ts b/src/auto-reply/reply/agent-runner.ts
index 7499657d6d4..bc7cbe4cb35 100644
--- a/src/auto-reply/reply/agent-runner.ts
+++ b/src/auto-reply/reply/agent-runner.ts
@@ -292,6 +292,7 @@ export async function runReplyAgent(params: {
       fallbackNoticeSelectedModel: undefined,
       fallbackNoticeActiveModel: undefined,
       fallbackNoticeReason: undefined,
+      memoryFlushContextHash: undefined,
     };
     const agentId = resolveAgentIdFromSessionKey(sessionKey);
     const nextSessionFile = resolveSessionTranscriptPath(
diff --git a/src/auto-reply/reply/memory-flush.ts b/src/auto-reply/reply/memory-flush.ts
index 95f6dbaa053..bad052531ee 100644
--- a/src/auto-reply/reply/memory-flush.ts
+++ b/src/auto-reply/reply/memory-flush.ts
@@ -1,3 +1,4 @@
+import crypto from "node:crypto";
 import { lookupContextTokens } from "../../agents/context.js";
 import { resolveCronStyleNow } from "../../agents/current-time.js";
 import { DEFAULT_CONTEXT_TOKENS } from "../../agents/defaults.js";
@@ -226,3 +227,20 @@ export function hasAlreadyFlushedForCurrentCompaction(
   const lastFlushAt = entry.memoryFlushCompactionCount;
   return typeof lastFlushAt === "number" && lastFlushAt === compactionCount;
 }
+
+/**
+ * Compute a lightweight content hash from the tail of a session transcript.
+ * Used for state-based flush deduplication — if the hash hasn't changed since
+ * the last flush, the context is effectively the same and flushing again would
+ * produce duplicate memory entries.
+ *
+ * Hash input: `messages.length` + content of the last 3 user/assistant messages.
+ * Algorithm: SHA-256 truncated to 16 hex chars (collision-resistant enough for dedup).
+ */
+export function computeContextHash(messages: Array<{ role?: string; content?: unknown }>): string {
+  const userAssistant = messages.filter((m) => m.role === "user" || m.role === "assistant");
+  const tail = userAssistant.slice(-3);
+  const payload = `${messages.length}:${tail.map((m, i) => `[${i}:${m.role ?? ""}]${typeof m.content === "string" ? m.content : JSON.stringify(m.content ?? "")}`).join("\x00")}`;
+  const hash = crypto.createHash("sha256").update(payload).digest("hex");
+  return hash.slice(0, 16);
+}
diff --git a/src/auto-reply/reply/session.ts b/src/auto-reply/reply/session.ts
index 6c1b2233c0f..a129af958b7 100644
--- a/src/auto-reply/reply/session.ts
+++ b/src/auto-reply/reply/session.ts
@@ -526,6 +526,9 @@ export async function initSessionState(params: {
     sessionEntry.compactionCount = 0;
     sessionEntry.memoryFlushCompactionCount = undefined;
     sessionEntry.memoryFlushAt = undefined;
+    // Clear stale context hash so the first flush in the new session is not
+    // incorrectly skipped due to a hash match with the old transcript (#30115).
+    sessionEntry.memoryFlushContextHash = undefined;
     // Clear stale token metrics from previous session so /status doesn't
     // display the old session's context usage after /new or /reset.
     sessionEntry.totalTokens = undefined;
diff --git a/src/config/sessions/types.ts b/src/config/sessions/types.ts
index 6513fc81b37..27acdf2aca7 100644
--- a/src/config/sessions/types.ts
+++ b/src/config/sessions/types.ts
@@ -164,6 +164,7 @@ export type SessionEntry = {
   compactionCount?: number;
   memoryFlushAt?: number;
   memoryFlushCompactionCount?: number;
+  memoryFlushContextHash?: string;
   cliSessionIds?: Record<string, string>;
   claudeCliSessionId?: string;
   label?: string;