Add commands, fix send-to-exited, improve docs

[pcarrier]

Summary

• Add blit wait ID --timeout N command that blocks until a PTY exits, returning its exit code (124 on timeout, matching GNU timeout convention)
• Add --pattern REGEX flag to wait that matches against new output produced after the wait begins (avoids stale matches from old scrollback)
• Add --wait --timeout N flags to blit start for inline blocking (blit start --cols 200 --wait --timeout 60 make -j8)
• Fix blit send silently dropping input to exited sessions — now returns an error
• Fix wait --pattern hanging on already-exited PTY when pattern doesn't match
• Document restart scrollback behavior (reuses session ID, does not clear terminal state)
• Document --ssh tunneling mechanism (SSH stdin/stdout relay to remote Unix socket via nc/socat, with connection multiplexing)
• Strengthen history size warning — emphasize always using --from-end 0 --limit N
• Replace polling loop documentation in SKILLS.md with blit wait examples

Motivation

Every agent using blit reinvents the same polling loop to wait for command completion, and most get the sleep interval or retry count wrong. blit wait collapses 4-5 lines of bash into one. start --wait further reduces the most common pattern to a single command. The send-to-exited bug causes silent confusion. The doc gaps around restart, SSH, and history size were identified in external feedback.

Testing

10 new tests added to the existing MockServer-based test infrastructure:

Test	What it verifies
test_send_to_exited_session	send returns error for exited PTY
test_wait_already_exited	Immediate return when PTY already exited at connect
test_wait_exits_later	Recv loop picks up S2C_EXITED and returns exit code
test_wait_timeout	Returns 124 when deadline fires
test_wait_not_found	Error for nonexistent PTY
test_wait_signal_exit	Signal exit maps to 128+N
test_wait_pattern_match	Regex match in terminal output exits 0
test_wait_pattern_exits_before_match	PTY exits before pattern matches, returns exit code
test_wait_pattern_already_exited_no_match	Already-exited PTY returns exit status instead of hanging
test_wait_invalid_pattern	Bad regex returns error

All 57 tests pass. cargo build clean.

Tag @indent to continue the conversation here.

[indent]

PR Summary

Adds a blit wait ID --timeout N command that blocks until a PTY exits (returning its exit code) or until output matches a --pattern REGEX. Also adds --wait --timeout N flags to blit start for inline blocking in a single command. Fixes blit send to error when targeting exited sessions, and updates SKILLS.md documentation throughout.

• New cmd_wait function with two modes: exit-wait (returns process exit code) and pattern-match (subscribes to output, returns 0 on match)
• blit start --wait --timeout N starts a PTY and blocks until it exits, opening a second connection for the wait logic
• cmd_start return type changed from Result<(), String> to Result<u16, String> to expose the created PTY ID
• Timeout returns exit code 124 (matching GNU timeout convention); signal exits mapped to 128+signal
• cmd_send now returns an error when the target session has already exited
• Added regex crate dependency for pattern matching
• Comprehensive test coverage for wait scenarios: already-exited, exits-later, timeout, not-found, signal exit, pattern match/no-match, invalid pattern, send-to-exited, and pattern on already-exited PTY
• SKILLS.md updated with wait and start --wait usage, restart scrollback warning, SSH tunneling details, and output conventions

Issues

All clear! No issues remaining. 🎉

1 issue already resolved

• cmd_wait with --pattern on an already-exited PTY will hang until timeout if the pattern doesn't match the frozen viewport. The non-pattern branch correctly checks conn.exited before looping, but the pattern branch skips this check. After subscribing, the server sends one initial update (the frozen terminal state), but if the pattern isn't found, no further updates or exit events arrive, so the loop blocks until the deadline. (fixed by commit 2cb5bb2)

CI Checks

All CI checks passed on commit 2cb5bb2.