fix(coding-agent): honor cross-project fork confirmations

[realsigridjin]

Summary

• settle an answered cross-project session confirmation before closing readline, so y and yes reach the fork path
• extend the issue fix(coding-agent): fail fast on cross-project --session with non-interactive stdin #756 regression through the real createSessionManager() interactive branch and verify the fork gets a new ID and the current-project cwd
• document the fork-specific core change in packages/coding-agent/src/changes.md and the user-facing fix in the coding-agent changelog

Regression

#756 added a close fallback for unanswered confirmations. Node's readline emits close synchronously, so the previous rl.close()-then-resolve(answer) order let the fallback settle the promise as false first. An affirmative response therefore printed Aborted. instead of forking.

The production fix is the minimal ordering change: settle the parsed answer, then close readline. Cancel, empty-input, EOF, non-interactive, local-session, and explicit --fork behavior remain unchanged.

Prior work

Supersedes #1042, opened by @beengineer500, which identified the readline close-ordering race and proposed settling the confirmation before closing readline. This adaptation rebases that fix onto current main and covers it through the existing #756 cross-project session regression using the real session-fork path, without exporting the confirmation helper.

Validation

• RED on current main: the new affirmative regression printed Aborted. and never emitted SESSION_FORKED
• GREEN with this patch: focused issue fix(coding-agent): fail fast on cross-project --session with non-interactive stdin #756 regression, 3/3
• related session-manager plus regression tests, 6/6
• npm run check
• npm run build
• Biome on the changed TypeScript files
• git diff --check
• isolated zero-token senpi-qa gates:
  • common self-check, 9/9
  • RPC self-test, 4/4
  • mock-loop self-test, 48/48
  • TUI smoke, 5/5
  • CLI smoke, 8/8
• built-CLI manual QA:
  • y created one fork with a new ID and target-project cwd
  • n and an empty answer aborted without a fork
  • an unknown session ID exited 1
  • --help exposed the session and fork options