test(coderd/x/chatd/chatprompt): table the text and error tool result rows in memory - #30945

TestMediaToolResultRoundTrip wrote a chat and two messages to PostgreSQL for every tool result codec case, although the read policy under test (toolResultPartToMessagePart) is pure. This PR moves the eight text-fallback and error cases into TestMediaToolResultConversion, an in-memory table, and deletes their database subtests: TextResultStaysText, MissingMimeTypeStaysText, MissingDataStaysText, ErrorResultStaysError, NonMediaResultTypeStaysText and the three IsMediaTrueBut* cases. The table encodes the same assistant tool call and tool result with MarshalParts and CurrentContentVersion, then runs ConvertMessagesWithFiles. The layer above moves the media rows.

Why it is safe

• Every row keeps its assertions. Each row also gains checks for role, part count, ToolCallID and ProviderExecuted=false, and text rows compare the output to a literal with JSONEq. ErrorResultStaysError compares the whole error message, and IsMediaTrueButMissingMimeType carries valid base64, so it fails on the mime_type check itself rather than in the base64 branch.
• I ran 24 mutants of chatprompt.go with go test -overlay against the tests on main, on this PR and on test(coderd/x/chatd/chatprompt): table the media codec matrix in memory #30946 (list below). Every mutant that main catches, this PR catches too. Three that survive on main fail here, and one (IsMedia winning over IsError) survives everywhere.

Review focus

The shared assertions in the table loop. The rows also stop passing through PostgreSQL, whose jsonb normalizes key order, whitespace, number forms and escapes, so production decodes different bytes than these rows feed in, with the same meaning. The deleted subtests and the new rows both compare with JSONEq, and the round trip the stack keeps covers media results only.

Validation

• go test ./coderd/x/chatd/chatprompt/ -count=1 -p 4 -parallel 4: ok on main and on this PR
• go vet ./coderd/x/chatd/chatprompt/: ok
• golangci-lint run --fix=false ./coderd/x/chatd/chatprompt/: 0 issues
• pre-commit hook: passed

Stack

The stack moves the tool result codec matrix out of PostgreSQL and keeps one storage round trip.

1. test(coderd/x/chatd/chatprompt): table the text and error tool result rows in memory #30945 table the text and error tool result rows in memory (this PR)
2. test(coderd/x/chatd/chatprompt): table the media codec matrix in memory #30946 table the media codec matrix in memory

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