test(coderd/x/chatd/chatdebug): table the stream wrapper tests and cover their status rules - #30980

Replaces five stream wrapper tests with two tables that run every case against both wrapStreamSeq and wrapObjectStreamSeq. #30981 rewrites both wrappers on one finalize-once lifecycle, and these tests pin what that rewrite must keep. It deletes TestWrapStreamSeq_CompletedNotDowngradedByCtxCancel, TestWrapObjectStreamSeq_CompletedNotDowngradedByCtxCancel, TestWrapStreamSeq_DroppedStreamFinalizedOnCtxCancel and TestDebugModel_StreamObjectRejectsNilSequence.

• New TestStreamWrapperStatus runs 13 cases on each wrapper: a finished stream, a consumer that stops before or after the finish part, a stream that ends without one, an error part with and without an error, an error on a text part, a consumer that stops after an error, a canceled error part, cancellation before the finish part and while the consumer holds it, a dropped stream, and a consumer that stops right after cancellation, which races the context safety net. Each case writes through a recording store and checks that the step is written exactly once, plus its status, finish reason, stored usage (all six token counts, or NULL), error count, last error, and whether the wrapper or the safety net finalized it.
• TestDebugModel_StreamRejectsNilSequence is now one table over Stream and StreamObject.
• TestDebugModel_Stream also checks the streamed text, not only that the response has content.

Why it is safe: the PR changes only a test file, and the tests pass on the production code of the layer below. To show they can fail, I ran 46 mutants of both wrappers and the nil-sequence checks. The whole package kills 17 of them before this PR and all 46 after it. The 29 it missed include the object wrapper's dropped-stream path, the rule that a stream without a finish part is interrupted, both error-part rules, cancellation while the consumer holds the finish part, text that is never materialized, usage that keeps only the input tokens or is stored without a finish part, and summary metadata on the safety net's write. Two more mutants drop the safety net's finalized check, so a step can be written twice. Across repeated batches of 50 runs, the race case kills them in 49 to 50 of 50 without -race. Under -race the kill rate depends on machine load: batches of 50 ranged from 24 to 46 kills. The unchanged code passes 200 runs with and without -race. A copy of model.go with garbage in it fails to build, which shows the mutants replaced the real file.

Review focus: the PR adds 117 more lines than it deletes. It is the test-first layer for #30981, which deletes 65 production lines.

Moved onto the deletion stack: a merge commit moved this layer onto the updated #30934 without a force push; its only conflict was the test file's import block (#30988 dropped time with the heartbeat tests). A second commit adds the audit follow-ups: the recording store, the stored usage check, the race case and the text check.

Validation: go test -race -count=1 ./coderd/x/chatd/chatdebug/... passes, golangci-lint run --fix=false ./coderd/x/chatd/chatdebug/... reports 0 issues, and the pre-commit hook passed.

Stack

This stack deletes the stale debug-run sweep, then simplifies the chatdebug debug-run, stream wrapper and step numbering code, drops the indexes the sweep used, and last deletes a runner debug field that lost its only reader with the heartbeats. The debug-run and stream wrapper refactors each sit on a test-only layer that pins the behavior they keep.

1. refactor(coderd): delete the chat debug run and step heartbeats #30988 Delete the chat debug run and step heartbeats
2. refactor: delete chatdebug FinalizeStale and the stale threshold #30989 Delete FinalizeStale and the stale threshold
3. refactor: delete the FinalizeStaleChatDebugRows query #30995 Delete the FinalizeStaleChatDebugRows query
4. test(coderd/x/chatd): pin the debug runs that turns, titles and status labels record #30933 Pin the debug runs that turns, titles and status labels record
5. refactor(coderd/x/chatd): create and finalize debug runs through one helper #30934 Create and finalize debug runs through one helper
6. This PR: Table the stream wrapper tests and cover their status rules
7. refactor(coderd/x/chatd/chatdebug): share one finalize-once lifecycle between the stream wrappers #30981 Share one finalize-once lifecycle between the stream wrappers
8. refactor(coderd): number chat debug steps in the database #31007 Number chat debug steps in the database
9. refactor(coderd/x/chatd/chatdebug): delete the process-global step counters #31008 Delete the process-global step counters
10. chore(coderd/database): drop the chat debug stale-sweep indexes #31009 Drop the chat debug stale-sweep indexes
11. refactor(coderd/x/chatd): drop the unused runnerCtx from the runner debug turn #31010 Drop the unused runnerCtx from the runner debug turn

Xum, an AI agent, opened this PR for @ibetitsmike and wrote this description.