EW-6888 Improve finishScheduled() outcome reporting

[fhanau]

Fixes a number of footguns that could lead to misleading event outcomes being reported for all events that use finishScheduled() (scheduled, queue, test etc.):

• Exception outcomes in finishScheduled() could be converted into exceededCpu
• Exception details were not being checked in finishScheduled()
• IoContext::taskFailed() now properly handles exception details
• Consolidate code used to get outcome from exception detail
• Add a TODO for improving outcome reporting when the scheduled time limit is hit

For context, see the recent outcome related changes (#6668, #6589, #6542) as well as the corresponding downstream PRs.

[ask-bonk]

I'm Bonk, and I've done a quick review of your PR.

This PR changes finishScheduled() to return EventOutcome directly instead of the internal FinishScheduledResult enum, improving outcome reporting by propagating richer error information from outcomeFromException().

Issues found (ranked by severity):

1. [HIGH] All three new DetailTypeId constants are placeholder 0x0ull — they collide with each other and will cause incorrect dispatching in outcomeFromException().
2. [MEDIUM] Leftover commented-out code and bare // TODO comments appear to be debug artifacts that should not be merged.
3. [LOW] The outcomeFromException function takes a non-const lvalue reference but doesn't modify the exception — should be const.

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This review was generated by an AI assistant and may contain inaccuracies.

[ask-bonk]

Review posted on PR #6606 with 4 inline comments. Summary of findings:

1. [HIGH] Three new DetailTypeId constants (SCRIPT_KILLED_DETAIL_ID, INACTIVE_WEBSOCKETS_DETAIL_ID, SCRIPT_NOT_FOUND_DETAIL_ID) are all 0x0ull — they collide with each other, making the branching logic in outcomeFromException() broken. All existing IDs in the codebase use unique random 64-bit values.

2. [MEDIUM] Leftover debug artifacts — bare // TODO comments and a commented-out old code line (// if (result == IoContext_IncomingRequest::FinishScheduledResult::TIMEOUT)) in queue.c++:967.

3. [LOW] outcomeFromException takes a mutable reference but doesn't modify the exception — should be const kj::Exception&.

github run

[codecov-commenter]

Codecov Report

❌ Patch coverage is 47.36842% with 20 lines in your changes missing coverage. Please review.
✅ Project coverage is 66.58%. Comparing base (1f09441) to head (a7c34a1).

Files with missing lines	Patch %	Lines
src/workerd/io/observer.c++	43.75%	4 Missing and 5 partials ⚠️
src/workerd/api/queue.c++	33.33%	3 Missing and 1 partial ⚠️
src/workerd/io/io-context.c++	50.00%	4 Missing ⚠️
src/workerd/io/worker-entrypoint.c++	57.14%	0 Missing and 3 partials ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #6606      +/-   ##
==========================================
+ Coverage   66.55%   66.58%   +0.02%     
==========================================
  Files         402      402              
  Lines      115890   115858      -32     
  Branches    19405    19396       -9     
==========================================
+ Hits        77131    77142      +11     
+ Misses      27188    27143      -45     
- Partials    11571    11573       +2     

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[codspeed-hq]

Merging this PR will not alter performance

✅ 72 untouched benchmarks
⏩ 129 skipped benchmarks¹

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_{Comparing felix/041726-outcome-reporting (a7c34a1) with main (1f09441)}

Footnotes

1. 129 benchmarks were skipped, so the baseline results were used instead. If they were deleted from the codebase, click here and archive them to remove them from the performance reports. ↩