feat: Implement Phase 4 Trigger Events System

- Added a new event-driven system for reactive storytelling, allowing rules like "When X happens, do Y."
- Introduced TriggerArea class for placeable sensors in the stage.
- Enhanced StickmanRig to emit signals for actions and arrivals.
- Updated StageDirectorVisuals to render rules visually with labels and badges.
- Modified StageSpawner to support spawning TriggerAreas.
- Improved text baseline calculations in speech bubbles and rule labels.
- Added tests for text baseline fixes to ensure proper rendering.
- Documented the implementation plan for Phase 4 in PHASE_4_TRIGGER_EVENTS.md.
- Created a polish plan for Phase 4 in PHASE_4b_POLISH.md.

docs/tech_debt_and_optimizations.md

@@ -23,6 +23,7 @@ This document tracks known technical debt, optimization opportunities, and minor
 | 11  | **Stage Freeze Abstraction** — Sandbox Stage EDIT‑mode freezing is type‑specific: `RigidBody2D.freeze_mode = FREEZE_MODE_KINEMATIC` for props, `StickmanRig.set_ragdoll(false)` for stickmen, nothing for `StaticBody2D` terrain. There is no unified "freeze" abstraction over the mixed physics population. | Low         | Open   | A future physics type (e.g. `Area2D`‑based sensors) will need another case in `scripts/sandbox_stage.gd` `_enter_edit_mode()` / `_enter_play_mode()`. Consider a duck‑typed `set_simulating(bool)` interface once more physical object kinds appear. (2026‑08‑27) |
 | 12  | **Stage AABB Selection Precision** — `StageSelection.get_world_aabb` uses conservative world‑space AABBs (polygon point union / fixed rig rect), not point‑in‑polygon.                                          | Low         | Open   | Clicks in the bounding‑box corners of large or rotated terrain may select a block even outside its polygon, and overlapping blocks can mis‑select. Refine with `Geometry2D.is_point_in_polygon()` for `TerrainBlock`/`PropBlock` polygons (and circle distance for ball props) once selection precision matters. (2026‑08‑27) |
 | 13  | **Slope-aware walking physics & dynamic obstacle avoidance (deferred)** — Phase 3a bakes a real navigation mesh (per-`TerrainBlock` polygon decomposition into a code-built `NavigationRegion2D`) and `walk_to` follows `NavigationAgent2D` paths, but the figure walks the path with an upright pose (no tilt to the slope, no physics sliding) and `avoidance_enabled = false`, so it can path through props and other stickmen. | Medium      | Open   | A stickman crossing a ramp/stair follows the sloped footprint but looks flat-footed, and does not avoid moving props or each other. Future: tilt/rotate the figure to the path slope and enable RVO avoidance (`avoidance_enabled`, avoidance layers, `velocity` handling) once props/other stickmen are registered as obstacles. (2026‑08‑29) |
+| 14  | **Phase 4 event engine is O(rigs×props + areas×movables) per physics frame** — `sandbox_stage.gd` `_update_area_entry()` / `_update_stickman_prop_collision()` run all-pairs geometric tests every physics frame in PLAY. | Low         | Open   | Fine at sandbox scale, but degrades quadratically with dozens of dynamic objects. Future: add a spatial hash / broadphase grid keyed by world cell to cull candidate pairs before the AABB/feet-point tests. (2026‑08‑30) |
 
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@@ -56,6 +57,7 @@ This document tracks known technical debt, optimization opportunities, and minor
 | 2026-08-27 | Sandbox Stage Builder (Phase 2) added `scripts/sandbox_stage.gd` + `stage_spawner.gd` / `stage_selection.gd` / `stage_gizmos.gd` + `scenes/sandbox_stage.tscn`. Logged #11 (no unified freeze abstraction over the mixed `StaticBody2D` / `RigidBody2D` / `Node2D` population) and #12 (selection hit‑testing uses world‑space AABBs rather than point‑in‑polygon). |
 | 2026-08-29 | Phase 3a (Core Director Functionality) spec written (`docs/phase_3a_spec.md`). Logged #13 (slope-aware walking physics + dynamic obstacle avoidance deferred — the nav mesh itself is built in 3a). Notable non-debt decisions recorded in the spec: Play mode now runs the director script instead of auto-ragdolling stickmen; `walk_to(target)` treats `target` as a feet/ground destination via `FOOT_OFFSET`, with the `NavigationAgent2D` child placed at the feet `(0,+385)` so it paths on the ground-level nav mesh. |
 | 2026-08-29 | **`walk_to` stops-after-a-few-px bug fixed.** `_update_walking` (Phase 3a) now defers nav reads until `NavigationServer2D.map_get_iteration_id(...) != 0` (map-sync guard) and forces the path query via `get_next_path_position()` before any empty-path/finished check. **Follow-up (same day):** the initial "warn + finish in place" unreachable-target policy was itself reported as "stickman stands still with a waypoint" and was replaced by **hybrid nav/direct steering** — an on-mesh target follows the nav path (`_walk_mode = "nav"`), an off-mesh/unreachable target walks **straight to the clicked waypoint** (`_walk_mode = "direct"`, root target = waypoint + `FOOT_OFFSET`), with **no** `push_warning`; `_walk_path_grace` removed (map-sync guard + forced path query replace it); the debug trace now carries `mode=nav|direct`. Off-by-default `DEBUG_WALK` (`stickman_rig.gd`) / `DEBUG_STAGE` (`sandbox_stage.gd`) traces added. #13 remains **Open** (slope physics + RVO avoidance are still deferred; the fix only changes unreachable-target handling). Logged in `BUGS.md`; verified with a 44-assertion headless regression suite. |
+| 2026-08-30 | Phase 4 (Triggers & Event System) implemented: `scripts/trigger_area.gd` (NEW placeable sensor), `sandbox_stage.gd` rule system (`_event_rules`, geometric event engine `_update_area_entry` / `_update_stickman_prop_collision`, rule-builder UI state machine, `_cleanup_rules_for_nodes`), `stickman_rig.gd` (`arrived` gains a `target` payload; new `enqueue_reactive`), `prop_block.gd` (`collided` physics signal), `stage_director_visuals.gd` rule visualization, `stage_spawner.gd` / `stage_selection.gd` `"area"` palette + duck-typed `get_area_rect`. Logged #14 (all-pairs event engine scales O(rigs×props + areas×movables); spatial hash suggested). |
 
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