test(coderd/x/chatd): move the Anthropic guard unit test into its own file - #30968

Moves TestAnthropicProviderToolPreRequestGuard out of coderd/x/chatd/chatd_test.go into a new coderd/x/chatd/anthropic_guard_test.go in the same package. The test calls chatsanitize.ApplyAnthropicProviderToolGuard on in-memory messages and builds no server or database. Giving it its own file lets the next PR move it into chatsanitize as a git rename. The end-to-end TestActiveServer_AnthropicProviderToolPreRequestGuard stays in chatd_test.go.

Why it is safe

This is a pure move, with no edits. The helpers the test uses stay in chatd_test.go for now; the next PR moves them.

• Purity check: diff <(git diff B H | grep '^-[^-]' | cut -c2- | sort) <(git diff B H | grep '^+[^+]' | cut -c2- | sort) prints only the new file's package clause, import (, ) and import paths. git diff --color-moved=plain marks all 137 removed lines as moved; the only 12 added lines it leaves unmarked are that package clause and import block.
• The same four subtests pass before and after: non_Anthropic_providers_are_unchanged, orphan_provider_result_is_textified, valid_provider_history_is_unchanged, logs_removals.

Review focus

Nothing changed outside the new file's header. git diff --color-moved=plain shows this at a glance.

Validation

• go test ./coderd/x/chatd/ -run '^TestAnthropicProviderToolPreRequestGuard$' -count=1 -v: 4 of 4 subtests pass.
• go vet ./coderd/x/chatd/: clean.
• Pre-commit hook (make pre-commit: gen, fmt, lint/go, lint/go/new-code, slim build): passed.

Stack

This stack moves the Anthropic guard unit test into chatsanitize, then deletes the guard escalation that can never repair a prompt.

1. test(coderd/x/chatd): move the Anthropic guard unit test into its own file #30968 Move the Anthropic guard unit test into its own file
2. test(coderd/x/chatd): move the Anthropic guard unit test into chatsanitize #30969 Move the Anthropic guard unit test into chatsanitize
3. refactor(coderd/x/chatd/chatsanitize): drop Anthropic guard escalation passes #30970 Drop the Anthropic guard escalation passes

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