Recognize home-relative Codex working directories

[matthiasplappert]

What changed

• accept both absolute (/workspace) and home-relative (~/Code/st2) working-directory paths in the Codex idle-footer classifier
• add a regression case for the home-relative footer rendered by current Codex sessions

Why

The DING sidecar only submits a notification after it can positively identify an empty, idle Codex composer. That classifier required the footer to contain · /, but current Codex sessions can shorten paths under the user's home directory to · ~/....

As a result, an otherwise idle composer was classified as ambiguous. The fail-closed delivery logic correctly withheld Return, but notifications remained queued and agents were never awakened. This caused delegated work to stall even though the sidecars and PTYs were healthy.

Recognizing the equivalent home-relative footer restores delivery without weakening the other idle-state checks.

Validation

• cargo +1.95.0 test ding
• targeted rustfmt --check for the two changed files
• installed the local build, restarted only DING sidecars, and observed a real notification wake an idle Codex session whose footer used ~/...

[matthiasplappert]

See screenshot for why this matters; the path starts with ~/ and not / hence the current failure