fix(hooks): presence_gate keys per-branch via hook_data cwd; engine propagates block exit code (FPLAN-0289 P1)

Activation fixes for the single-session presence gate. Two bugs blocked it,
both caught by live testing after all units were green:

1) Wrong branch key. presence_gate used Path.cwd().name, but under the Claude
   Code bridge the hook process cwd is the project root, so every session keyed
   to "AIPass": the gate never enforced one-live-session-per-branch and would
   have rejected sessions project-globally (any 2nd interactive session in any
   branch). Now _resolve_branch(hook_data) reads the event payload's cwd (the
   real session dir) and walks up to the branch root (.trinity/ or apps/),
   mirroring branch_loader. Applied in handle() and handle_stop().

2) Block never reached Claude Code. engine.dispatch() returned only stdout, so
   the bridge could not surface a non-zero exit. dispatch() now returns
   (stdout, exit_code) and the bridge exits with it on a block. Pre-existing gap
   affecting every block hook on every event; now fixed engine-wide. An
   intentional block (exit 2 + {"decision":"block"}) propagates; a crashing hook
   (exit 2, non-JSON stdout) is logged and falls through, so the gate fails open.

Proven: 110 hooks unit tests pass (6 new for branch resolution); seedgo @hooks
100%, no type errors. Live bridge end-to-end (real live holder + real bridge):
duplicate into a held branch -> exit 2 + block reason naming the branch; a
different free branch -> exit 0 (per-branch isolation intact). Gate remains
dormant: not yet wired into provider settings.

Design: DPLAN-0225 / FPLAN-0289 P1 activation. Build by @hooks.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01CqoxFdbDMirzkQ5kjRVVos

src/aipass/hooks/apps/modules/engine.py

@@ -89,17 +89,17 @@ def _matches(matcher: str, value: str) -> bool:
     return value in matcher.split("|")
 
 
-def dispatch(event_type: str, stdin_data: str, config: dict) -> str:
-    """Core dispatch — run hooks for event, return merged stdout."""
+def dispatch(event_type: str, stdin_data: str, config: dict) -> tuple[str, int]:
+    """Core dispatch — run hooks for event, return (merged_stdout, exit_code)."""
     if not config.get("hooks_enabled", True):
         logger.info("[HOOKS] all hooks disabled")
         _log({"ts": time.time(), "event": event_type, "action": "all_hooks_disabled"})
-        return ""
+        return "", 0
 
     event_hooks = config.get(event_type, {})
     if not event_hooks:
         _log({"ts": time.time(), "event": event_type, "action": "no_hooks_configured"})
-        return ""
+        return "", 0
 
     match_value = ""
     parsed = {}
@@ -196,7 +196,7 @@ def dispatch(event_type: str, stdin_data: str, config: dict) -> str:
                         "total_ms": round(total_ms, 1),
                     }
                 )
-                return result["stdout"]
+                return result["stdout"], 2
 
             logger.error(
                 "[HOOKS] %s.%s CRASHED exit=2: %s",
@@ -229,7 +229,7 @@ def dispatch(event_type: str, stdin_data: str, config: dict) -> str:
         }
     )
 
-    return "\n".join(outputs)
+    return "\n".join(outputs), 0
 
 
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