diff --git a/packages/core/src/base.ts b/packages/core/src/base.ts
index e8ad49ce0..903671fa3 100644
--- a/packages/core/src/base.ts
+++ b/packages/core/src/base.ts
@@ -35,14 +35,14 @@ async function repositoryBase(folder: string, root: string): Promise<BaseUnit> {
  * repository Tesota's snapshot of it. Verification reads this record and
  * never rebuilds the base after the agent changed the files.
  */
-export async function captureBase(cwd: string): Promise<Base> {
+export async function captureBase(cwd: string, signal?: AbortSignal): Promise<Base> {
   const units = workspaceUnits(cwd);
   const workspace = units.some(({ folder }) => folder !== "");
   const found: BaseUnit[] = [];
   for (const { folder, repository } of units) {
     const root = join(cwd, folder);
     if (repository) { found.push(await repositoryBase(folder, root)); continue; }
-    const snapshot = await takeSnapshot(root, workspace && folder === "", withLockWhile);
+    const snapshot = await takeSnapshot(root, workspace && folder === "", withLockWhile, undefined, signal);
     found.push("refused" in snapshot ? { folder, kind: "refused", reason: snapshot.refused }
       : { folder, kind: "snapshot", commit: snapshot.base, tooLarge: snapshot.tooLarge });
   }
diff --git a/packages/core/src/loop.ts b/packages/core/src/loop.ts
index 8ff91a161..8e744e4c5 100644
--- a/packages/core/src/loop.ts
+++ b/packages/core/src/loop.ts
@@ -33,7 +33,7 @@ export interface LoopOptions {
   /** What a resumed session already holds; a new session starts empty. */
   readonly resumed?: LoopState;
   /** The base of a request; the gate's units (`captureBase`) when not given. */
-  readonly captureBase?: (cwd: string) => Promise<Base>;
+  readonly captureBase?: (cwd: string, signal: AbortSignal) => Promise<Base>;
   /** The session's extensions; they settle before the verifier and cannot replace it. */
   readonly extensions?: readonly ExtensionFactory[];
   /** What verifies each run before it may complete (#439); a run whose verifier has no settle handler never completes. */
@@ -745,7 +745,7 @@ export function createLoop(options: LoopOptions): LoopSession {
   async function start(run: number, text: string, origin: Origin, signal: AbortSignal): Promise<void> {
     const at = new Date().toISOString();
     const written = (async () => {
-      writer.append({ type: "request", run, text, origin, at, base: await base(options.cwd) });
+      writer.append({ type: "request", run, text, origin, at, base: await base(options.cwd, signal) });
       writer.sync();
     })();
     recorded = written.catch(() => undefined);
diff --git a/packages/core/src/session-lock.ts b/packages/core/src/session-lock.ts
index c3305360a..e8f75cffc 100644
--- a/packages/core/src/session-lock.ts
+++ b/packages/core/src/session-lock.ts
@@ -110,11 +110,15 @@ export function withLock<T>(path: string, work: () => T): T {
 /**
  * Runs `work`, which may wait on the network, holding the lock at `path`,
  * waiting up to `waitMs` for another holder in this process or another
- * (#459): an MCP token refresh, which a second at once would spend.
+ * (#459): an MCP token refresh, which a second at once would spend. A
+ * `signal` that stops ends the wait, refused as the lock being held; work
+ * that already holds the lock runs to its end, so the lock is never released
+ * under it.
  */
-export async function withLockWhile<T>(path: string, work: () => Promise<T>, waitMs: number): Promise<T> {
+export async function withLockWhile<T>(path: string, work: () => Promise<T>, waitMs: number, signal?: AbortSignal): Promise<T> {
   const until = Date.now() + waitMs;
-  const waiting = Schedule.spaced(50).pipe(Schedule.while(({ input }) => input instanceof SessionLockedError && Date.now() < until));
+  const waiting = Schedule.spaced(50).pipe(Schedule.while(({ input }) =>
+    input instanceof SessionLockedError && Date.now() < until && signal?.aborted !== true));
   const acquire = Effect.retry(Effect.try({ try: () => lockSession(path), catch: (error) => error }), waiting);
   return Effect.runPromise(Effect.acquireUseRelease(acquire,
     () => Effect.tryPromise({ try: work, catch: (error) => error }),
diff --git a/packages/core/tests/snapshot.test.ts b/packages/core/tests/snapshot.test.ts
index cb7a7ea49..7109ddcd3 100644
--- a/packages/core/tests/snapshot.test.ts
+++ b/packages/core/tests/snapshot.test.ts
@@ -1,5 +1,5 @@
 import { expect, test } from "bun:test";
-import { mkdtempSync, readdirSync, rmSync, writeFileSync } from "node:fs";
+import { mkdirSync, mkdtempSync, readdirSync, rmSync, writeFileSync } from "node:fs";
 import { tmpdir } from "node:os";
 import { join } from "node:path";
 import { git } from "../../../src/git.ts";
@@ -72,3 +72,36 @@ test("two processes snapshot one fresh folder together", async () => {
     rmSync(root, { recursive: true, force: true });
   }
 });
+
+test("a stop while the snapshot store is held by another ends the request at once, with no snapshot taken", async () => {
+  const { createModels, fauxProvider } = await import("@earendil-works/pi-ai");
+  const { createSession } = await import("../src/session.ts");
+  const { lockSession } = await import("../src/session-lock.ts");
+  const { tesotaHome } = await import("../../../src/home.ts");
+  const { scriptedReply, accepts } = await import("./scripted.ts");
+  const root = mkdtempSync(join(tmpdir(), "tesota-core-snapshot-"));
+  writeFileSync(join(root, "notes.txt"), "hello\n");
+  mkdirSync(tesotaHome(), { recursive: true });
+  // Another session's snapshot holds the store, which a request waits for up to 30 s.
+  const held = lockSession(join(tesotaHome(), "snapshots.lock"));
+  const faux = fauxProvider();
+  faux.setResponses(["done"].map(scriptedReply));
+  const models = createModels();
+  models.setProvider(faux.provider);
+  const session = createSession({ cwd: root, folder: mkdtempSync(join(tmpdir(), "tesota-core-sessions-")), models, model: faux.getModel(),
+    verifier: accepts });
+  try {
+    const run = session.prompt("go");
+    await new Promise((resolve) => setTimeout(resolve, 300));
+    const stopped = performance.now();
+    await session.abort();
+    await run;
+    expect(performance.now() - stopped).toBeLessThan(5_000);
+    expect(session.outcome()).toBe("aborted");
+    expect(session.ledger()[0]?.base.units).toEqual([{ folder: "", kind: "refused", reason: "the run was stopped before the snapshot was taken" }]);
+  } finally {
+    held.release();
+    await session.dispose();
+    rmSync(root, { recursive: true, force: true });
+  }
+}, 60_000);
diff --git a/src/host.ts b/src/host.ts
index fa0a864ed..5af376105 100644
--- a/src/host.ts
+++ b/src/host.ts
@@ -11,7 +11,7 @@ export interface HostParts {
   /** The POSIX shell the project's checks run in: its path and arguments, and whether it reads the command from its input instead. */
   readonly shellConfig: () => { shell: string; args: string[]; commandTransport?: "argv" | "stdin" };
   /** Runs asynchronous work under an OS lock, waiting up to `waitMs` for another writer in this process or another. */
-  readonly withLockWhile: <T>(path: string, work: () => Promise<T>, waitMs: number) => Promise<T>;
+  readonly withLockWhile: <T>(path: string, work: () => Promise<T>, waitMs: number, signal?: AbortSignal) => Promise<T>;
 }
 
 let given: HostParts | undefined;
diff --git a/src/snapshot.ts b/src/snapshot.ts
index 9ba72b8f0..ae533e0ff 100644
--- a/src/snapshot.ts
+++ b/src/snapshot.ts
@@ -106,7 +106,7 @@ export function homeOrDriveRoot(folder: string): boolean {
  * `ownFiles`. A home folder or a drive's root is never snapshotted.
  */
 export async function takeSnapshot(root: string, ownFiles: boolean, withLockWhile: HostParts["withLockWhile"],
-  limits: SnapshotLimits = SNAPSHOT_LIMITS): Promise<Snapshot> {
+  limits: SnapshotLimits = SNAPSHOT_LIMITS, signal?: AbortSignal): Promise<Snapshot> {
   const at = resolve(root);
   if (homeOrDriveRoot(at)) return { refused: "Tesota does not snapshot a home folder or a drive's root" };
   const tooLarge = scan(at, ownFiles, limits);
@@ -115,7 +115,12 @@ export async function takeSnapshot(root: string, ownFiles: boolean, withLockWhil
   const gitDir = join(snapshots, createHash("sha256").update(`${at}\0${ownFiles}`).digest("hex").slice(0, 16));
   mkdirSync(snapshots, { recursive: true });
   // One writer for the store (#461): pruning also removes other folders. The lock stays outside what it prunes.
+  // A stop ends the wait for the store, and no Git step starts after it; one under way is short and runs to its end.
+  const stopped = { refused: "the run was stopped before the snapshot was taken" };
+  const isStopped = (): boolean => signal?.aborted === true;
+  if (isStopped()) return stopped;
   return withLockWhile(join(tesotaHome(), "snapshots.lock"), async () => {
+    if (isStopped()) return stopped;
     useSnapshotGit(at, gitDir);
     if (!existsSync(join(gitDir, "HEAD"))) {
       mkdirSync(gitDir, { recursive: true });
@@ -126,11 +131,15 @@ export async function takeSnapshot(root: string, ownFiles: boolean, withLockWhil
     writeFileSync(join(gitDir, "info", "exclude"), [...excludedFolders.map((name) => `${name}/`), ".env", ".env.*",
       ...ownFiles ? ["/*/"] : [], ...tooLarge.map(exactly)].join("\n"));
     writeFileSync(join(gitDir, "tesota-used"), at);
+    if (isStopped()) return stopped;
     const committed = await git(at, ["-c", "advice.addEmbeddedRepo=false", "add", "-A"]) !== undefined
       && await git(at, ["-c", "user.name=Tesota", "-c", "user.email=tesota@localhost", "commit", "-q", "--allow-empty",
         "--no-verify", "-m", "Tesota snapshot"]) !== undefined;
     const base = committed ? (await git(at, ["rev-parse", "HEAD"]))?.trim() : undefined;
     prune(snapshots);
     return base === undefined || base === "" ? { refused: "Git could not make a snapshot of it" } : { base, tooLarge };
-  }, 30_000);
+  }, 30_000, signal).catch((error: unknown) => {
+    if (isStopped()) return stopped;
+    throw error;
+  });
 }