[o11y] Add internalError event outcome

[fhanau]

See internal discussion as for the rationale for this.
As noted in outcome.capnp, the authoritative version of EventOutcome is defined internally and needs to be updated first – this has already been done.
Note that internalError is not being used in workerd at present – we likely will use it in server.c++'s RequestObserverWithTracer::reportFailure(), but we should only start using it there once we've finalized how it will be used in the edge runtime.

Also see the internal PR.

[ask-bonk]

The changes are clean, complete, and consistent. Let me verify one more thing - whether the ToJs switch in trace-stream.c++ is exhaustive (all enum values are covered):

The switch statement in trace-stream.c++:312-337 covers all 12 enum values (OK, CANCELED, EXCEPTION, KILL_SWITCH, DAEMON_DOWN, EXCEEDED_CPU, EXCEEDED_MEMORY, LOAD_SHED, RESPONSE_STREAM_DISCONNECTED, SCRIPT_NOT_FOUND, INTERNAL_ERROR, UNKNOWN), which matches the 12 values in outcome.capnp. The new INTERNAL_ERROR case is placed in correct alphabetical order (after SCRIPT_NOT_FOUND, before UNKNOWN), consistent with the ordering pattern of the switch.

The TypeScript type union in trace.d.ts is updated, and the generated snapshots match. The capnp ordinal @11 is correctly one past the previous maximum @10.

This is a minimal, well-structured addition of a new enum variant across all the right layers. No behavioral changes, no backward compatibility concerns (additive only), no security implications.

LGTM

github run

[codspeed-hq]

Merging this PR will not alter performance

✅ 72 untouched benchmarks
⏩ 129 skipped benchmarks¹

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_{Comparing felix/041526-internal-error (d615a50) with main (5fdf8aa)}

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. ↩

[codecov-commenter]

Codecov Report

❌ Patch coverage is 0% with 2 lines in your changes missing coverage. Please review.
✅ Project coverage is 66.48%. Comparing base (5fdf8aa) to head (d615a50).

Files with missing lines	Patch %	Lines
src/workerd/io/trace-stream.c++	0.00%	1 Missing and 1 partial ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #6589   +/-   ##
=======================================
  Coverage   66.47%   66.48%           
=======================================
  Files         405      405           
  Lines      117773   117775    +2     
  Branches    19424    19425    +1     
=======================================
+ Hits        78295    78297    +2     
+ Misses      27900    27898    -2     
- Partials    11578    11580    +2     

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