[P2] Bound SDK token acquisition and cleanup waits #26

Review finding R7, priority P2. Reviewed source: e112e51.

Assessment

Scores are engineering estimates, not calibrated probabilities or CVSS. Confidence rates improvement from the proposed fix; severity reflects this repository's prerequisites and safeguards. Higher difficulty/code-size scores mean more work.

The deadline gap is reproduced against the real SDK, but a safe solution must handle uncertain and late create results plus cleanup. This needs a technical design step before implementation.

Finding and verification

Evidence: The wrapper passes signals to exec/upload/download but directly awaits their SDK promises (src/sandbox/render/client.ts:97,122,126). The installed SDK first requests a connect token without the passed signal. Its control-plane client has no configured HTTP deadline. Termination is also awaited without a cleanup budget at line 144. The existing comment in sandbox.ts:94 acknowledges create/get limitations but does not cover these additional phases.

Trigger and verification: Using the real pinned SDK with a process-local fake transport, a token response delayed 80 ms held a nominal 5 ms exec deadline for approximately 83 ms. The token request had no supplied signal. A separate host probe showed a 25 ms provision budget still pending at 70 ms while a 180 ms create call was in flight.

Impact: A stalled token request can exceed application deadlines before the signal-aware data plane begins. A stalled cleanup can delay returning an already computed answer. Outer workflow and provider lifetime backstops remain useful, but do not make these host waits bounded.

Fix direction: Use a supported provider-owned bounded HTTP transport or upstream signal support for token/control-plane requests, plus a cleanup budget. Preserve eventual cleanup of uncertain or late create results; a bare Promise.race that forgets the eventual creation can leak resources until provider timeout.

Current SDK check: This gap remains in the versioned SDK 1.4.0 source. The public Render constructor has no fetch/timeout option; the exported SandboxesClient accepts a provider-owned API transport. Details and public API constraints are in the current SDK source and public constructor contract.

Regression: Delay each token phase and termination independently. Verify bounded return, no model work after cancellation, and cleanup of a late-created Sandbox. Exercise the real SDK transport, not only a fake method that already honors a signal.

Proposed implementation scope

SDK transport adapter/client, deadline and cleanup handling, real-transport contract tests, possible explicit transport dependency; roughly 4–7 files.

Keep this fix separate from unrelated refactors. Preserve the qualifications above; no real Render or paid model validation was performed during review.

Acceptance and verification

• Add the focused regression described above and confirm it detects the current behavior.
• Implement the selected fix without changing unrelated public behavior.
• Run frozen dependency installation, pnpm typecheck, and the relevant existing tests; report failures and skipped checks.
• Update docs/config migration where affected.
• Record any required Render staging or snapshot-refresh validation before rollout.

Use a dedicated codex/issue-N-sandbox-transport-deadlines branch and a focused PR referencing this issue after the fix is selected.