fix(cli): preserve attached run output

[rekram1-node]

Issue for this PR

Found during live CLI testing. Related to the local-run fix in #31389.

Type of change

• Bug fix
• New feature
• Refactor / code improvement
• Documentation

What does this PR do?

run --attach can exit 0 before printing the final answer because the prompt request finishes before its event reader catches up.

After a successful attached request, cancel/drain the event reader and replay missing output from the saved messages for that prompt. Reuse the existing renderer and deduplicate completed parts. This adds one history read per attached prompt/command, but does not depend on receiving an idle event. Local runs and immediate request-error handling stay unchanged.

How did you verify your code works?

• Subprocess tests cover normal streaming, a connected stream withholding every event, tool/reasoning ordering, resumed sessions, commands, and request errors.
• bun test test/cli/run/run-process.test.ts --rerun-each 3: 48 passed.
• bun typecheck, Prettier, and git diff --check passed.
• Live Anthropic and Bedrock Opus 5 read-tool runs both emitted the exact saved final answer and exactly one final step_finish, using isolated databases.

Screenshots / recordings

Not a UI change.

Checklist

• I have tested my changes locally
• I have not included unrelated changes in this PR