diff --git a/src/session/assemble-runtime.ts b/src/session/assemble-runtime.ts
index 9998f8f61..8e7960c5c 100644
--- a/src/session/assemble-runtime.ts
+++ b/src/session/assemble-runtime.ts
@@ -557,11 +557,11 @@ export interface ChatAgentWiring {
    */
   getCompactor: (wrapPruning?: (pruning: Compactor) => Compactor) => Compactor;
   /**
-   * Bound to the TUI compaction lifecycle abort signal. The completeness
-   * gate runs inside wrapCompactor's race, so a discarded certified stub
-   * must not persist a compaction-handoff for a fold that never landed.
+   * Bound to the TUI compaction lifecycle abort signal. Captured at
+   * completeness-gate apply start so onBuilt reset() cannot un-abort an
+   * in-flight fold that wrapCompactor already discarded.
    */
-  isCompactionAborted?: () => boolean;
+  getCompactionAbortSignal?: () => AbortSignal;
   /** Experimental Anthropic prompt shrink. Default off when omitted. */
   anthropicCachePrompt?: () => boolean;
   /**
@@ -795,9 +795,9 @@ export function assembleChatAgent(wiring: ChatAgentWiring): AssembledChatAgent {
                 wrapCompactorWithCompletenessGate(
                   pruning,
                   primaryArchive,
-                  wiring.isCompactionAborted === undefined
+                  wiring.getCompactionAbortSignal === undefined
                     ? undefined
-                    : { isAborted: wiring.isCompactionAborted },
+                    : { getSignal: wiring.getCompactionAbortSignal },
                 ),
         ),
       },
diff --git a/src/session/compaction-archive.ts b/src/session/compaction-archive.ts
index c00a58a2a..40487af4d 100644
--- a/src/session/compaction-archive.ts
+++ b/src/session/compaction-archive.ts
@@ -952,16 +952,21 @@ async function recordFreshHandoffOutput(
  * drop it even when the summarizer does not echo it verbatim. `isAborted`
  * skips that record: the TUI wrapCompactor race can discard a certified
  * stub, and a handoff for a fold that never landed is a phantom.
+ * `getSignal` is captured at apply start so onBuilt `reset()` cannot
+ * un-abort an in-flight fold that wrapCompactor already discarded.
  */
 export function wrapCompactorWithCompletenessGate(
   inner: Compactor,
   archive: CompactionArchive,
-  opts?: { isAborted?: () => boolean },
+  opts?: { isAborted?: () => boolean; getSignal?: () => AbortSignal },
 ): Compactor {
   return {
     name: inner.name,
     version: inner.version,
     async apply(turns: ConversationTurn[], ctx: StrategyContext) {
+      const abortSignal = opts?.getSignal?.();
+      const isAborted = () =>
+        abortSignal?.aborted === true || opts?.isAborted?.() === true;
       await archive.awaitPendingWrites();
       const proposed = await inner.apply(turns, ctx);
       const units = uncoveredContentUnits(turns, proposed.output);
@@ -988,14 +993,14 @@ export function wrapCompactorWithCompletenessGate(
       if (certificate.status !== "complete") {
         return incompleteIdentity(inner, turns);
       }
-      if (opts?.isAborted?.() === true) {
+      if (isAborted()) {
         return proposed;
       }
       await recordFreshHandoffOutput(
         archive,
         turns,
         proposed.output,
-        opts?.isAborted,
+        isAborted,
       );
       return proposed;
     },
diff --git a/src/session/runtime-assembly.test.ts b/src/session/runtime-assembly.test.ts
index c3eeb0942..324a08475 100644
--- a/src/session/runtime-assembly.test.ts
+++ b/src/session/runtime-assembly.test.ts
@@ -985,6 +985,111 @@ describe("createSessionPruningCompactor stub fallback", () => {
     );
     expect(handoffs).toEqual([]);
   });
+
+  test("abort then reset during certifyRange does not record a phantom handoff", async () => {
+    const notices: string[] = [];
+    const folds: { stub: boolean }[] = [];
+    const summarize = createModelSummarizer({
+      getSource: () =>
+        ({
+          id: "test",
+          provider: "openai",
+          model: "test-model",
+          baseURL: "http://localhost:1",
+          credentialId: "test",
+        }) as never,
+      complete: async () => {
+        throw new Error("model unreachable");
+      },
+    });
+    const dir = await mkdtemp(join(tmpdir(), "compaction-gate-abort-reset-"));
+    const blobs = new Map<string, Uint8Array>();
+    const archive = createCompactionArchive({
+      sessionId: "sess-gate-abort-reset",
+      contextDir: dir,
+      writeBlob: async (key, bytes) => {
+        blobs.set(key, bytes);
+      },
+      readBlob: async (key) => {
+        const bytes = blobs.get(key);
+        if (bytes === undefined) throw new Error(`missing ${key}`);
+        return bytes;
+      },
+    });
+    const now = Date.now();
+    const many = Array.from({ length: 8 }, (_, i) => ({
+      role: (i % 2 === 0 ? "user" : "assistant") as "user" | "assistant",
+      content: [{ type: "text" as const, text: `t${i}` }],
+      timestamp: now,
+    }));
+    for (const turn of many) {
+      const block = turn.content[0];
+      if (block?.type !== "text") continue;
+      await archive.recordAuthorizedPayload({
+        kind: turn.role === "assistant" ? "assistant_text" : "user_message",
+        payload: block.text,
+      });
+    }
+    const lifecycle = createCompactionLifecycle();
+    const getSignal = () => lifecycle.getSignal();
+    const isAborted = () => lifecycle.getSignal().aborted;
+    let releaseGated: () => void = () => undefined;
+    const gatedFinished = new Promise<void>((resolve) => {
+      releaseGated = resolve;
+    });
+    const abortingArchive = {
+      ...archive,
+      certifyRange: async (ids: readonly string[]) => {
+        const certificate = await archive.certifyRange(ids);
+        lifecycle.abortCompaction("operator interrupt");
+        // onBuilt reset() mints a fresh controller; the in-flight apply
+        // must still treat this compact as aborted.
+        lifecycle.reset();
+        return certificate;
+      },
+    };
+    const wrapped = lifecycle.wrapCompactor(
+      createSessionPruningCompactor({
+        summarize,
+        onFolded: (info) => folds.push(info),
+        onFailure: (text) => notices.push(text),
+        getSignal,
+        isAborted,
+        compactionShape: { tailBudgetTokens: 1 },
+        wrapPruning: (pruning) => {
+          const gated = wrapCompactorWithCompletenessGate(
+            pruning,
+            abortingArchive,
+            { getSignal, isAborted },
+          );
+          return {
+            name: gated.name,
+            version: gated.version,
+            apply: async (turns, ctx) => {
+              try {
+                return await gated.apply(turns, ctx);
+              } finally {
+                releaseGated();
+              }
+            },
+          };
+        },
+      }),
+    );
+    const result = await wrapped.apply(many as never, {
+      state: {} as never,
+      trigger: "test",
+    });
+    await gatedFinished;
+    expect(result.output).toBe(many);
+    expect(result.record.reason).toBe(COMPACTION_ABORTED_REASON);
+    expect(folds).toEqual([]);
+    expect(notices).toEqual([]);
+    const handoffs = (await archive.listOccurrences()).filter(
+      (occurrence) => occurrence.provenance === "compaction-handoff",
+    );
+    expect(handoffs).toEqual([]);
+  });
 });
 
 describe("buildCompactionContinuationMessage", () => {
diff --git a/src/session/runtime-assembly.ts b/src/session/runtime-assembly.ts
index 51e937b86..d0a1e5167 100644
--- a/src/session/runtime-assembly.ts
+++ b/src/session/runtime-assembly.ts
@@ -441,6 +441,12 @@ export interface SessionPruningCompactorArgs {
    * no onFolded side effects for work that never landed.
    */
   isAborted?: () => boolean;
+  /**
+   * Captured at apply start. Prefer this over a live `isAborted` that
+   * re-reads getSignal(): onBuilt reset() replaces the controller, and a
+   * discarded in-flight fold must still look aborted.
+   */
+  getSignal?: () => AbortSignal;
   /**
    * Wraps the inner pruning apply before fold-commit side effects.
    * assembleChatAgent passes the completeness gate here so a discarded
@@ -513,15 +519,15 @@ export function createSessionPruningCompactor(
       pendingStubNotice = undefined;
       const turnsBefore = turns.length;
       const startedAt = Date.now();
+      const abortSignal = args.getSignal?.();
+      const isAborted = () =>
+        abortSignal?.aborted === true || args.isAborted?.() === true;
       const result = await compactor.apply(turns, ctx);
       // A discarded compact reports nothing. When the lifecycle abort wins
       // the outer race, this inner run may still complete with a genuine
       // fold — but the reactor threw that output away, so emitting telemetry
       // or onFolded would describe work that never landed (phantom fold).
-      if (
-        args.isAborted?.() === true ||
-        result.record.reason === COMPACTION_ABORTED_REASON
-      ) {
+      if (isAborted() || result.record.reason === COMPACTION_ABORTED_REASON) {
         return result;
       }
       // summarizedTurnCount is only set on the branch that actually folded
diff --git a/src/tui/runner/session.ts b/src/tui/runner/session.ts
index 1b3d21c67..bd01a6219 100644
--- a/src/tui/runner/session.ts
+++ b/src/tui/runner/session.ts
@@ -697,7 +697,7 @@ export async function assembleTUISession(
         ? state.liveDefaultSource
         : state.liveSource.id,
     anthropicCachePrompt: () => config.anthropicCachePrompt,
-    isCompactionAborted: () => compactionLifecycle.getSignal().aborted,
+    getCompactionAbortSignal: () => compactionLifecycle.getSignal(),
     getCompactor: (wrapPruning) =>
       compactionLifecycle.wrapCompactor(
         createSessionPruningCompactor({
@@ -710,8 +710,9 @@ export async function assembleTUISession(
             ),
           // The outer abort race discards this run's output — a fold that
           // still completes underneath must not report telemetry or side
-          // effects for work that never landed.
-          isAborted: () => compactionLifecycle.getSignal().aborted,
+          // effects for work that never landed. Capture the signal at apply
+          // start: onBuilt reset() replaces the live controller.
+          getSignal: () => compactionLifecycle.getSignal(),
           // Stub notice waits until the fold commits (verify abort and
           // completeness-gate discard stay silent).
           onFailure: (text) => state.systemNotice?.(text),