fix(modal): surface repo image build failure details

[hreiten]

Summary

• Preserve structured setup/supervisor failure details when a repo image build exits before image_build.complete
• Redact the clone token and repo environment variable values before storing build failure messages
• Fix supervisor.fatal logging so it does not collide with the reserved LogRecord.message field

Why

Repo image builds currently fall back to Build sandbox exited without completing (exit_code=...) even when the build sandbox already emitted a more useful structured failure such as setup.failed or supervisor.error. That makes failed image builds hard to diagnose from the settings UI.

There is also a separate fatal-error logging path that passes message= through logging.extra, which raises KeyError: "Attempt to overwrite 'message' in LogRecord" before the fatal error can be reported.

Validation

• cd packages/modal-infra && ./.venv/bin/ruff check . && ./.venv/bin/ruff format --check . && ./.venv/bin/pytest tests/ -q
• cd packages/sandbox-runtime && ./.venv/bin/ruff check . && ./.venv/bin/ruff format --check . && ./.venv/bin/pytest tests/ -q
• npm run lint
• npm run typecheck

npm test currently fails in unrelated control-plane model tests for GPT 5.5 default reasoning expectations; this PR does not touch TypeScript model metadata or tests.

Summary by CodeRabbit

• Bug Fixes
  • Improved image build failure reporting: captures concise error messages from build logs, trims long messages, and redacts sensitive values; sandbox exits now report extracted errors instead of generic messages.
  • Fixed supervisor fatal-error reporting to use the correct structured field for the error message.
• Tests
  • Updated and added tests to validate failure reporting, truncation, and redaction behavior.

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: defaults

Review profile: CHILL

Plan: Pro

Run ID: 78a41982-c4ff-47ab-92cf-00b2a1809423

📥 Commits

Reviewing files that changed from the base of the PR and between d3a4ce4 and be9088d.

📒 Files selected for processing (4)

• packages/modal-infra/src/scheduler/image_builder.py
• packages/modal-infra/tests/test_image_builder_v2.py
• packages/sandbox-runtime/src/sandbox_runtime/entrypoint.py
• packages/sandbox-runtime/tests/test_supervisor_monitor.py

🚧 Files skipped from review as they are similar to previous changes (4)

• packages/sandbox-runtime/tests/test_supervisor_monitor.py
• packages/sandbox-runtime/src/sandbox_runtime/entrypoint.py
• packages/modal-infra/tests/test_image_builder_v2.py
• packages/modal-infra/src/scheduler/image_builder.py

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📝 Walkthrough

Walkthrough

Streams structured build logs, extracts a concise redacted/truncated failure message when present, returns (sha, complete, error) from the log streamer, and raises BuildError with the extracted message if the sandbox exits without completion; aligns supervisor fatal logging field and updates tests.

Changes

Image Build Error Reporting Enhancement

Layer / File(s)	Summary
Failure message extraction utilities packages/modal-infra/src/scheduler/image_builder.py	Adds Iterable import, constants BUILD_FAILURE_MESSAGE_MAX_CHARS, BUILD_FAILURE_REDACT_MIN_CHARS, _BUILD_LOG_EVENTS, _SETUP_FAILURE_EVENTS, and helpers _format_build_failure_event and _trim_build_failure_message to extract and redact concise failure messages from structured JSON log events.
Stream build logs refactor packages/modal-infra/src/scheduler/image_builder.py	Rewrites _stream_build_logs(sandbox, redact_values) to parse structured JSON stdout, capture head_sha from git.sync_complete, treat image_build.complete as completion, select setup/supervisor payloads for concise error text, and return (head_sha, build_complete, error_message).
Build pipeline integration packages/modal-infra/src/scheduler/image_builder.py	build_repo_image now collects redact_values (clone token and injected env values), passes them into _stream_build_logs, and raises BuildError with the extracted build_error if the sandbox exits without completion.
Test coverage for stream logs contract packages/modal-infra/tests/test_image_builder_v2.py	Tests updated to await the new 3-tuple and assert error is None on success; _build_handle expanded to accept stdout_lines and returncode; new test test_reports_build_log_failure_when_stream_never_completes verifies redaction/truncation and failure callback payload.
Fatal error reporting field alignment packages/sandbox-runtime/src/sandbox_runtime/entrypoint.py, packages/sandbox-runtime/tests/test_supervisor_monitor.py	SandboxSupervisor._report_fatal_error now emits the fatal message under error_message (not message); new test TestFatalErrorReporting ensures reporting does not collide with reserved fields.

Estimated code review effort

🎯 3 (Moderate) | ⏱️ ~25 minutes

Possibly related PRs

• ColeMurray/background-agents#636: Modifies build_repo_image and sandbox termination in image build failure handling; closely related to this PR's error extraction and reporting changes.
• ColeMurray/background-agents#503: Related changes to how error_message is extracted/redacted from build-log events and surfaced to UI.

Suggested reviewers

• open-inspect

Poem

🐇 I stitched the logs with careful art,

hid the secrets, trimmed the part,
masked the tokens, kept the clue,
now builds can tell us what they do —
hop in, reviewers, take a cart!

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 71.43% which is insufficient. The required threshold is 80.00%.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (4 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title clearly and specifically describes the main change: surfacing detailed error information from failed repo image builds instead of using generic messages.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

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✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests

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[coderabbitai]

Actionable comments posted: 1

🤖 Prompt for all review comments with AI agents

Verify each finding against current code. Fix only still-valid issues, skip the
rest with a brief reason, keep changes minimal, and validate.

Inline comments:
In `@packages/modal-infra/src/scheduler/image_builder.py`:
- Around line 53-63: The failure events list is missing "supervisor.fatal", so
update the constants: add "supervisor.fatal" to the _BUILD_LOG_EVENTS tuple and
include it in the _BUILD_FAILURE_EVENTS set (which is _SETUP_FAILURE_EVENTS |
{...}) so supervisor.fatal is treated as a build/fatal error; this will allow
_stream_build_logs and the error-extraction logic that inspects supervisor
events to pick up the structured fatal messages instead of falling back to
generic failures.

🪄 Autofix (Beta)

Fix all unresolved CodeRabbit comments on this PR:

• Push a commit to this branch (recommended)
• Create a new PR with the fixes

---

ℹ️ Review info

⚙️ Run configuration

Configuration used: defaults

Review profile: CHILL

Plan: Pro

Run ID: 018208cd-7e99-4263-9a04-6fc34f4838bf

📥 Commits

Reviewing files that changed from the base of the PR and between a8a14c4 and 3f5574b.

📒 Files selected for processing (4)

• packages/modal-infra/src/scheduler/image_builder.py
• packages/modal-infra/tests/test_image_builder_v2.py
• packages/sandbox-runtime/src/sandbox_runtime/entrypoint.py
• packages/sandbox-runtime/tests/test_supervisor_monitor.py