fix: scope the machine-global mode flag by project so concurrent sessions stop clobbering each other (#662)

[ousamabenyounes]

Summary

Fix #662

Live ponytail mode lives in one machine-global .ponytail-active file, so two Claude Code sessions in different repos clobber each other:

1. Repo A configured full writes the flag; a concurrent repo B configured off then injects the ruleset into every subagent it spawns, despite being off.
2. Starting a session in repo B calls clearMode(), deleting the flag out from under repo A's still-running session — A's subagents silently stop receiving the ruleset.

Fix — attribute the flag to its writer. setMode() records the writing project in a .ponytail-active.owner sidecar keyed by CLAUDE_PROJECT_DIR (which Claude Code sets per session). Two changes use it:

• clearMode() refuses to delete a flag owned by a different project — fixes consequence 2.
• The SubagentStart hook ignores the flag only when this repo defaults off and doesn't own it — fixes consequence 1.

Ownership only whitelists: an explicit /ponytail opt-in in an otherwise-off repo owns the flag and still injects, so a legitimately-active session is never suppressed. Unknown project (non-Claude hosts, which use their own per-host state dir anyway) falls back to the legacy unscoped behavior, and runtime /ponytail toggles keep driving subagents unchanged.

Test verification (RED → GREEN)

New assertions in tests/hooks.test.js cover: an off repo ignores a foreign flag, a self-owned opt-in still injects, clearMode won't delete a foreign flag, and a same-repo off session still clears its own.

RED — both hooks at unmodified main, new tests applied:

# AssertionError [ERR_ASSERTION]: an off repo must ignore another repo's active flag (#662)
#     at tests/hooks.test.js:378
# pass 0
# fail 1

GREEN — full suite with the fix:

# tests 107
# pass 106
# fail 1   (pre-existing: "csv: correct pandas one-liner" needs `pip install pandas`, which CI installs)

node scripts/check-rule-copies.js and node scripts/check-versions.js both pass.

Files changed

File	Change
hooks/ponytail-runtime.js	.ponytail-active.owner sidecar; owner-aware clearMode; ownedByCurrentProject
hooks/ponytail-subagent.js	ignore a foreign flag when this repo defaults off and doesn't own it
tests/hooks.test.js	4 ownership scenarios for concurrent cross-repo sessions