test(coderd): run the TestPostChats workspace, input, and MCP rejections on one server - #30976

This PR moves the remaining 9 isolated rejection subtests of TestPostChats into the shared Rejects table from the previous PR: the 4 workspace cases, EmptyText, UnsupportedPartType, RejectsInvalidReasoningEffort, and the cross-org and third-org MCP server cases. Each one no longer starts its own coderd and AI Bridge daemon.

MCPServerIDsDisabledConfigRejected keeps its own server: after the create rejection it sends a message on a chat it creates, which a single-request case cannot express.

Why it is safe

• Cases keep the old subtest names, callers, status, and message checks, and now also check the exact Detail. The reasoning-effort case compares the full detail instead of two substrings.
• I mutated 12 lines in postChats and its workspace, input, effort, and MCP helpers and ran the old and new test files against each one. The old file caught 10 and the new file catches the same 10, each in the case that owns it, plus a detail-text mutant the old file missed. The one mutant both survive (reading the workspace as system) returns the same response from the SSH check.

Review focus

The workspace and input cases now run with the shared default model present. postChats rejects them before it resolves a model, so the model does not change their result. The MCP cases add their configs to orgs that no other case reads, or to the default org with default_off, where no other case passes MCP IDs.

Timing

From 5 alternating runs, the moved subtests took 2.83 s summed (median); their 9 cases take 0.27 s on the shared server. For the whole stack, go test reports 1.96 s instead of 3.19 s for the package.

Validation

• go test ./coderd -run '^TestPostChats$' -count=3: pass
• the same run with -race: pass
• go test -overlay mutant runs against the old and new test files: results above
• go vet ./coderd and golangci-lint run ./coderd/...: clean; the pre-commit hook passed

Stack

The stack runs every isolated TestPostChats rejection case on one shared server instead of one server per case.

1. test(coderd): run the TestPostChats model and org rejections on one server #30975 Model and organization rejection cases
2. test(coderd): run the TestPostChats workspace, input, and MCP rejections on one server #30976 Workspace, request input, and MCP server rejection cases (this PR)

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