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khaliqgant merged 2 commits into from
Oct 9, 2026
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feat(babysitter): keep the fixer's PR checkout across reused sandboxes (F3a) #635

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feat(babysitter): keep the fixer's PR checkout across reused sandboxe…
khaliqgant Oct 9, 2026
9aa6413
fix(babysitter): review round 1 on the PR checkout cache
khaliqgant Oct 9, 2026
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7 changes: 7 additions & 0 deletions examples/babysitter/FIXER.md
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Expand Up @@ -30,6 +30,13 @@ from #4226, and Cloud publishes server-side.
are removed: a previous agent turn may have written them.
- An existing checkout (a reused sandbox) is fetched, reset to the head and
cleaned in place. Ignored files, such as installed dependencies, survive.
- **Per-PR reuse (C2):** Cloud may hand a later wake the same sandbox.
Each run root is created anew, so the checkout lives in
`$HOME/.babysitter/<owner>/<repo>/<pr>/checkout` between runs. It is
moved (renamed, dependencies included) into the run root before
`checkoutHead`, and moved back after the run, whatever its outcome,
before `f.done`. If the cache is on another filesystem, or damaged, the
run starts fresh.
2. **One agent** (`babysitter-fix`, the origin session's CLI, with a literal
pinned model per CLI, ignoring the policy's `agentCli`) runs in that
checkout. Its task opens with the origin's first prompt, verbatim and
Expand Down
130 changes: 97 additions & 33 deletions examples/babysitter/artifacts/babysitter-fixer.flow.ts
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Expand Up @@ -607,8 +607,9 @@ var SUMMARY_MAX_CHARS = 4e3;
var REFUSED_PATHS = String.raw`^\.github/workflows/|(^|/)\.env($|\.)|\.(pem|key|p12|pfx|jks)$|(^|/)id_(rsa|dsa|ecdsa|ed25519)(\.pub)?$|(^|/)\.(npmrc|netrc|pypirc)$|(^|/)secrets?/`;
async function checkoutHead(c) {
const { execFileSync } = await import("node:child_process");
const { existsSync, mkdirSync, rmSync, writeFileSync } = await import("node:fs");
const { resolve } = await import("node:path");
const { createHash } = await import("node:crypto");
const { existsSync, mkdirSync, readdirSync, readFileSync, rmSync } = await import("node:fs");
const { join, resolve } = await import("node:path");
if (!process.env.GH_TOKEN) throw new Error("GH_TOKEN required");
const dir = resolve("babysitter-checkout");
const auth = Buffer.from(`x-access-token:${process.env.GH_TOKEN}`).toString("base64");
Expand All @@ -626,21 +627,69 @@ async function checkoutHead(c) {
GIT_CONFIG_VALUE_2: "false"
};
const git = (...args) => String(execFileSync("git", ["-C", dir, ...args], { env, encoding: "utf8", stdio: ["ignore", "pipe", "pipe"] })).trim();
const reused = existsSync(`${dir}/.git`);
if (!reused) {
mkdirSync(dir, { recursive: true });
git("init", "-q");
}
writeFileSync(`${dir}/.git/config`, "[core]\n repositoryformatversion = 0\n filemode = true\n bare = false\n");
rmSync(`${dir}/.git/hooks`, { recursive: true, force: true });
rmSync(`${dir}/.git/info/attributes`, { force: true });
git("fetch", "-q", "--no-tags", "--depth=50", `https://github.com/${c.owner}/${c.repo}.git`, c.head);
git("checkout", "-q", "--force", "--detach", c.head);
const MANIFESTS = /^(package\.json|package-lock\.json|npm-shrinkwrap\.json|pnpm-lock\.yaml|yarn\.lock|bun\.lockb?|requirements[\w.-]*\.txt|pyproject\.toml|poetry\.lock|Pipfile\.lock|uv\.lock|Cargo\.lock|go\.sum|Gemfile\.lock|composer\.lock)$/;
const SKIP = /* @__PURE__ */ new Set([".git", "node_modules", "vendor", "target", "dist", "build", ".venv", "venv"]);
const fingerprint = () => {
const hash = createHash("sha256");
const walk = (at, rel, depth) => {
if (depth > 6) return;
for (const entry2 of readdirSync(at, { withFileTypes: true }).sort((a, b) => a.name.localeCompare(b.name))) {

@cubic-dev-ai cubic-dev-ai Bot Oct 9, 2026

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P2: The cached tree is agent-writable, but fingerprinting propagates readdirSync and readFileSync errors before rebuilding the checkout. An unreadable directory or manifest therefore makes the next fixer run fail instead of starting fresh; treat fingerprint failures as a corrupt cache and fall back to a clean checkout.

Prompt for AI agents 
Check if this issue is valid — if so, understand the root cause and fix it. When an issue isn't valid or won't be fixed in this PR, reply in its thread with the reason and then resolve the thread. At examples/babysitter/artifacts/babysitter-fixer.flow.ts, line 636:

<comment>The cached tree is agent-writable, but fingerprinting propagates `readdirSync` and `readFileSync` errors before rebuilding the checkout. An unreadable directory or manifest therefore makes the next fixer run fail instead of starting fresh; treat fingerprint failures as a corrupt cache and fall back to a clean checkout.</comment>

<file context>
@@ -626,35 +627,47 @@ async function checkoutHead(c) {
+    const hash = createHash("sha256");
+    const walk = (at, rel, depth) => {
+      if (depth > 6) return;
+      for (const entry2 of readdirSync(at, { withFileTypes: true }).sort((a, b) => a.name.localeCompare(b.name))) {
+        if (entry2.isDirectory() && !SKIP.has(entry2.name)) walk(join(at, entry2.name), `${rel}${entry2.name}/`, depth + 1);
+        else if (entry2.isFile() && MANIFESTS.test(entry2.name)) hash.update(`${rel}${entry2.name}\0`).update(readFileSync(join(at, entry2.name))).update("\0");
</file context>

if (entry2.isDirectory() && !SKIP.has(entry2.name)) walk(join(at, entry2.name), `${rel}${entry2.name}/`, depth + 1);
else if (entry2.isFile() && MANIFESTS.test(entry2.name)) hash.update(`${rel}${entry2.name}\0`).update(readFileSync(join(at, entry2.name))).update("\0");
}
};
walk(dir, "", 0);
return hash.digest("hex");
};
const reused = existsSync(dir);
mkdirSync(dir, { recursive: true });
const before = fingerprint();
rmSync(join(dir, ".git"), { recursive: true, force: true });
git("init", "-q");
git("fetch", "-q", "--no-tags", "--depth=50", c.origin ?? `https://github.com/${c.owner}/${c.repo}.git`, c.head);
git("reset", "-q", "--hard", c.head);
git("clean", "-q", "-fd");
git("clean", "-q", reused && fingerprint() !== before ? "-fdx" : "-fd");
if (git("rev-parse", "HEAD") !== c.head) throw new Error("Checkout is not at the bound head");
process.stdout.write(JSON.stringify({ dir, head: c.head, reused }));
}
async function restoreCheckout(c) {
const { existsSync, renameSync, rmSync } = await import("node:fs");
const { homedir } = await import("node:os");
const { join, resolve } = await import("node:path");
const cache = join(c.home ?? homedir(), ".babysitter", c.owner.toLowerCase(), c.repo.toLowerCase(), String(c.number), "checkout");
const dir = resolve("babysitter-checkout");
let restored = false;
try {
if (existsSync(cache) && !existsSync(dir)) {
renameSync(cache, dir);
restored = true;
}
} catch {
try {
rmSync(cache, { recursive: true, force: true });

@cubic-dev-ai cubic-dev-ai Bot Oct 9, 2026

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P2: Concurrent runs for the same PR can delete each other's cached checkout: this removes a checkout another run may have just stashed before renaming its own. Serialize cache moves per PR so one run cannot discard another run's dependency cache.

Prompt for AI agents 
Check if this issue is valid — if so, understand the root cause and fix it. When an issue isn't valid or won't be fixed in this PR, reply in its thread with the reason and then resolve the thread. At examples/babysitter/artifacts/babysitter-fixer.flow.ts, line 657:

<comment>Concurrent runs for the same PR can delete each other's cached checkout: this removes a checkout another run may have just stashed before renaming its own. Serialize cache moves per PR so one run cannot discard another run's dependency cache.</comment>

<file context>
@@ -641,6 +641,42 @@ async function checkoutHead(c) {
+      renameSync(cache, dir);
+      restored = true;
+    } catch {
+      rmSync(cache, { recursive: true, force: true });
+    }
+  }
</file context>

@khaliqgant khaliqgant Oct 9, 2026

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Not applicable with cloud C2c (#4356). The per-PR lease admits one run at a time per PR and artifact (a concurrent wake gets a retryable babysitter_pr_sandbox_busy), and different sandboxes have different $HOMEs. So two runs never share a cache path concurrently. Without C2c each run gets a fresh box and nothing is cached.

} catch {
}
}
process.stdout.write(JSON.stringify({ restored }));
}
async function stashCheckout(c) {
const { existsSync, mkdirSync, renameSync, rmSync } = await import("node:fs");
const { homedir } = await import("node:os");
const { dirname, join, resolve } = await import("node:path");
const cache = join(c.home ?? homedir(), ".babysitter", c.owner.toLowerCase(), c.repo.toLowerCase(), String(c.number), "checkout");
const dir = resolve("babysitter-checkout");
let stashed = false;
try {
if (existsSync(dir)) {
rmSync(cache, { recursive: true, force: true });
mkdirSync(dirname(cache), { recursive: true });
renameSync(dir, cache);
stashed = true;
}
} catch {
}
process.stdout.write(JSON.stringify({ stashed }));
}
async function proposeChanges(c) {
const { execFileSync } = await import("node:child_process");
const { rmSync, writeFileSync } = await import("node:fs");
Expand Down Expand Up @@ -677,6 +726,12 @@ async function proposeChanges(c) {
if (Buffer.byteLength(out) > c.limits.proposalBytes) return refuse("proposal exceeds the journal output bound");
process.stdout.write(out);
}
async function restore(f, pr) {
return JSON.parse(await f.run(nodeCommand(restoreCheckout, { owner: pr.owner, repo: pr.repo, number: pr.number }), { timeout: "2m" })).restored === true;
}
async function stash(f, pr) {
await f.run(nodeCommand(stashCheckout, { owner: pr.owner, repo: pr.repo, number: pr.number }), { timeout: "2m" });
}
async function checkout(f, pr, head) {
const value = JSON.parse(await f.run(nodeCommand(checkoutHead, { owner: pr.owner, repo: pr.repo, head }), { timeout: "5m" }));
if (value.head !== head || typeof value.dir !== "string") throw new Error("Checkout did not report the bound head");
Expand Down Expand Up @@ -730,27 +785,36 @@ function createStandaloneFixer(policy, runtime = capabilities) {
);
if (!a) return;
const { pr, wake, origin, c, head, report } = a;
const work = await checkout(f, pr, head);
const task = agentTask(origin, `${pr.owner}/${pr.repo}#${pr.number}`, head, a.changed, "fix");
const result = origin.source === "codex" ? await f.agent("babysitter-fix", { cli: "codex", model: "gpt-5.6-sol", cwd: work.dir, permissions: { accessPreset: "readwrite" }, task }) : await f.agent("babysitter-fix", { cli: "claude", model: "claude-sonnet-5", cwd: work.dir, permissions: { accessPreset: "readwrite" }, task });
const final = await readState(f, c);
if (final.headSha !== head || outOfScope(final, c, configured.label)) {
await report(`${wake.id}: head moved or PR left scope while fixing; no proposal for ${head}`);
return f.done("declined");
}
const outcome = parseOutcome(result.summary);
const proposal = await propose(f, {
dir: work.dir,
head,
pullRequest: { owner: pr.owner, repo: pr.repo, number: pr.number },
summary: neutralise(outcome.summary, origin.firstPrompt).slice(0, SUMMARY_MAX_CHARS),
replies: threadReplies(a, outcome.replies)
});
if (proposal.kind === "babysitter-refusal") {
await report(`${wake.id}: proposal refused: ${proposal.reason}`);
return f.done("needs_human", { detail: `Babysitter proposal refused: ${proposal.reason}` });
await restore(f, pr);
let verdict;
try {
const work = await checkout(f, pr, head);
const task = agentTask(origin, `${pr.owner}/${pr.repo}#${pr.number}`, head, a.changed, "fix");
const result = origin.source === "codex" ? await f.agent("babysitter-fix", { cli: "codex", model: "gpt-5.6-sol", cwd: work.dir, permissions: { accessPreset: "readwrite" }, task }) : await f.agent("babysitter-fix", { cli: "claude", model: "claude-sonnet-5", cwd: work.dir, permissions: { accessPreset: "readwrite" }, task });
const final = await readState(f, c);
if (final.headSha !== head || outOfScope(final, c, configured.label)) {
await report(`${wake.id}: head moved or PR left scope while fixing; no proposal for ${head}`);
verdict = { reason: "declined" };
} else {
const outcome = parseOutcome(result.summary);
const proposal = await propose(f, {
dir: work.dir,
head,
pullRequest: { owner: pr.owner, repo: pr.repo, number: pr.number },
summary: neutralise(outcome.summary, origin.firstPrompt).slice(0, SUMMARY_MAX_CHARS),
replies: threadReplies(a, outcome.replies)
});
if (proposal.kind === "babysitter-refusal") {
await report(`${wake.id}: proposal refused: ${proposal.reason}`);
verdict = { reason: "needs_human", detail: `Babysitter proposal refused: ${proposal.reason}` };
} else {
verdict = { reason: "success", detail: `Babysitter proposal for ${head}: ${proposal.files.length} file(s)` };
}
}
} finally {
await stash(f, pr);
}
f.done("success", { detail: `Babysitter proposal for ${head}: ${proposal.files.length} file(s)` });
f.done(verdict.reason, verdict.detail ? { detail: verdict.detail } : void 0);
};
return subscriptions.reduce(
(handle, subscription) => handle.on(subscription.trigger, body),
Expand Down
4 changes: 2 additions & 2 deletions examples/babysitter/artifacts/babysitter-fixer.manifest.json
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@@ -1,8 +1,8 @@
{
"schemaVersion": 1,
"artifact": "babysitter-fixer.flow.ts",
"bytes": 41908,
"sha256": "797ce37d24831fd4ed8091020ef18a5e3a77f1e18605f6648e315a096a1a6cc6",
"bytes": 44812,
"sha256": "d69e3e4f511cba1c668438101a2fb7540fc3fc97b31a0c0eb854fab1791a7487",
"policy": "../standalone-policy.json",
"policySha256": "e2fd08aaef4ea922146ad1330d7b7d7161f078f9c19e1499aa272636ae6e39a2",
"runtime": {
Expand Down
63 changes: 63 additions & 0 deletions examples/babysitter/evidence/f3-checkout-cache/01-red.txt
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@@ -0,0 +1,63 @@
# fix.ts/fixer.ts at 01149375; tests from the F3 commit.
$ node --experimental-strip-types --test tests/fixer.test.ts
✔ the fixer checks out the bound head, runs one agent there with fix rules, and journals one proposal (2.870232ms)
✔ the fixer never writes to GitHub itself: no push, merge, review, or comment calls (0.630366ms)
✔ thread replies go only to inline feedback this run was woken by, once each, marked and neutralised (0.535859ms)
✔ a head that moves while fixing declines without a proposal (0.317191ms)
✔ a refused proposal ends needs_human (0.397742ms)
✔ by default the fixer dispatches no agent and checks nothing out (gate 8 / #442) (0.938991ms)
✔ the agent outcome is read from a JSON message, a fenced JSON block, or falls back to prose (0.195023ms)
✔ a real proposal covers edits, new files and the agent's own commits, all against the bound head (72.917016ms)
✔ workflow, secret, oversized and too-wide proposals are refused whole (328.176771ms)
✔ an untouched checkout proposes an empty patch (replies and summary may still publish) (43.603598ms)
✔ the proposal script runs as f.run runs it: a stringified `node -e` command in a shell (75.060774ms)
✔ the proposal script lifted from the shipped artifact runs under `node -e` (72.127132ms)
✔ the proposal never runs code the agent planted in the checkout's git config, and its diff format is fixed (52.673283ms)
✔ paths git would have to quote are refused; a newline cannot split a name past the workflow rule (118.653171ms)
✔ a non-ASCII name is proposed unquoted, so Cloud parses the same path (42.946322ms)
✔ the fixer runs the origin session's own CLI with its literal pinned model (1.037575ms)
✖ a PR checkout survives between runs: restored into the run root, stashed back after (0.61106ms)
✖ the fixer restores the cached checkout before checking out, and stashes it even when the agent fails (1.443883ms)
ℹ tests 18
ℹ suites 0
ℹ pass 16
ℹ fail 2
ℹ cancelled 0
ℹ skipped 0
ℹ todo 0
ℹ duration_ms 934.900586

✖ failing tests:

test at tests/fixer.test.ts:267:1
✖ a PR checkout survives between runs: restored into the run root, stashed back after (0.61106ms)
TypeError: restoreCheckout is not a function
at file:///home/khaliqgant/Projects/AgentWorkforce/flows-worktrees/babysitter-f2/examples/babysitter/tests/fixer.test.ts:280:40
at capture (file:///home/khaliqgant/Projects/AgentWorkforce/flows-worktrees/babysitter-f2/examples/babysitter/tests/fixer.test.ts:276:17)
at TestContext.<anonymous> (file:///home/khaliqgant/Projects/AgentWorkforce/flows-worktrees/babysitter-f2/examples/babysitter/tests/fixer.test.ts:280:26)
at async Test.run (node:internal/test_runner/test:1409:7)
at async Test.processPendingSubtests (node:internal/test_runner/test:974:7)

test at tests/fixer.test.ts:297:1
✖ the fixer restores the cached checkout before checking out, and stashes it even when the agent fails (1.443883ms)
AssertionError [ERR_ASSERTION]: Expected values to be strictly deep-equal:
+ actual - expected

[
- 'restoreCheckout',
'checkoutHead',
'proposeChanges',
- 'stashCheckout'
]

at TestContext.<anonymous> (file:///home/khaliqgant/Projects/AgentWorkforce/flows-worktrees/babysitter-f2/examples/babysitter/tests/fixer.test.ts:301:10)
at async Test.run (node:internal/test_runner/test:1409:7)
at async Test.processPendingSubtests (node:internal/test_runner/test:974:7) {
generatedMessage: true,
code: 'ERR_ASSERTION',
actual: [ 'checkoutHead', 'proposeChanges' ],
expected: [ 'restoreCheckout', 'checkoutHead', 'proposeChanges', 'stashCheckout' ],
operator: 'deepStrictEqual',
diff: 'simple'
}
exit=1
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