Phase 3 — Decision pipeline + JobRunner + RestProvider + save round-trip

AI core (scenes/ai/, 5 new files from 3 gdscript-refactor agents in parallel):
- job.gd (59 lines, Agent A): Job class, RefCounted, label + toils + cursor +
  to_dict/from_dict round-trip
- toil.gd (76 lines, Agent A): Toil class, RefCounted; kinds WALK/WAIT/IDLE;
  factories walk_to/wait_ticks/idle; Vector2i stored as to_x/to_y ints
  because Godot 4 JSON.stringify doesn't round-trip Vector2i
- work_provider.gd (27 lines, Agent A): abstract base, class_name, @export
  category/priority, find_best_for() with push_error subclass guard
- job_runner.gd (186 lines, Agent B): Node-derived runner; setup/start_job/
  cancel_job/tick; WALK toil delegates to pawn.walk_along_path on first
  encounter (sets data.started=true), listens for walk_completed signal;
  WAIT decrements ticks_remaining; IDLE never completes; full to_dict/from_dict
- decision.gd (50 lines, Agent C): static pick_next_job(pawn, providers); 5
  layers (incapacitation/forced/status/work/idle); layer 1 probes via
  has_method to stay future-proof for Phase 9
- rest_provider.gd (31 lines, Agent C): extends WorkProvider; @export rest_tile;
  returns [walk_to(rest_tile), idle()] Job

Integration (Opus):
- pawn.gd: added forced_job slot, job_runner ref, _orchestrate_ai called
  before _advance_walk on each sim_tick. Calls Decision when forced_job is
  queued OR when idle — was a bug initially (only-on-idle never preempted
  the never-completing IDLE toil); fixed and caught via MCP runtime test.
  Added to_dict/from_dict for save round-trip; captures tile, _path,
  _step_progress, _selected, forced_job, job_runner via their serializers.
- selection.gd: rewrote to build a forced-job [walk_to + idle] and set
  pawn.forced_job; Decision preempts current job on next tick.
- world.tscn/gd: instantiates RestProvider as child (rest_tile = (50,50)
  just outside the stone ring's south-east, reachable from all 3 spawn
  tiles); registers via World.register_work_provider; attaches a JobRunner
  child to each spawned pawn and wires setup(pawn, pathfinder).
- world.gd autoload: added work_providers list + register/clear methods.
- save_system.gd: write_save walks World.pawns calling to_dict; apply_save
  zips dicts to pawns by index (Phase 16 will add stable IDs).
- main.gd: bootstrap log line bumped Phase 2 → Phase 3.

Acceptance — MCP-verified end-to-end:
- 3 pawns boot, Decision assigns each Rest, JobRunner starts each,
  all 3 walk to (50,50) on different paths (40/35/30 steps based on
  detour around the stone ring), arrive and idle.
- Force Bram to (10,10) via pawn.forced_job; preempt fires:
  [decision] Bram: forced 'Go to (10, 10)'. Bram walks while Cora/Edda
  stay parked.
- Mid-walk save round-trip (the critical Phase 3 acceptance):
  - Paused Bram at (51,10) walking to (70,70) with 79 path steps remaining
  - SaveSystem.write_save() → SaveSystem.apply_save(read_save()) after a
    mutate-to-(0,0)-with-no-path round-trip
  - Restored Bram exactly: tile=(51,10), _path.size=79, walking=true,
    job='Go to (70, 70)' at toil_idx=0 (WALK toil with data.started=true)
  - Resumed sim → JobRunner's WALK toil saw started=true and did NOT
    re-call walk_along_path; the pawn's restored _path continued the walk
    naturally → reached (70,26) with 44 steps remaining, still on the
    same job. The architecture.md 'mid-toil suspend safe' contract is
    provably honored.

Phase 3 gotchas (logged in implementation.md):
- Class-name registration timing bit again (Phase 2 gotcha). Workflow:
  agent writes class_name file → MCP reload_project → headless validate.
- Forced-job preempt requires triggering Decision when forced_job != null,
  not just when idle (IDLE toil never completes).
- execute_game_script + await Engine.get_main_loop().process_frame is
  flaky — MCP auto-recovers but the script's last lines may be lost.
  Workaround: split state-inspection into a fresh execute_game_script.

Delegation report this phase:
- gdscript-refactor (Sonnet) Agent A: Job + Toil + WorkProvider abstract
  base. 3 files, 162 lines.
- gdscript-refactor (Sonnet) Agent B: JobRunner with toil-execution match
  + walk_completed signal handling + full save round-trip. 1 file, 186
  lines.
- gdscript-refactor (Sonnet) Agent C: Decision pipeline + RestProvider.
  2 files, 81 lines.
- Opus: Pawn integration (forced_job slot, orchestration, to_dict/from_dict),
  Selection rewrite, world.tscn/gd wiring, World autoload work_providers
  list, SaveSystem extension, MCP-driven runtime verification including
  the mid-walk save round-trip demo, gotcha logging.

~70% of Phase 3's GDScript was written by subagents.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

scenes/ai/toil.gd

@@ -0,0 +1,76 @@
+class_name Toil extends RefCounted
+## A single atomic step within a Job — walk, wait, idle, etc.
+##
+## Save/load contract: every value in `data` MUST be JSON-safe.
+## Vector2i is NOT JSON-safe in Godot 4 — tile coordinates are stored as
+## "to_x"/"to_y" integer keys, never as Vector2i. get_walk_destination()
+## reconstructs Vector2i on demand.
+##
+## Round-trip invariant:
+##   var t2 := Toil.from_dict(t.to_dict())
+##   assert(t2.kind == t.kind and t2.done == t.done and t2.data == t.data)
+
+const KIND_WALK: StringName = &"walk"
+const KIND_WAIT: StringName = &"wait"
+const KIND_IDLE: StringName = &"idle"
+
+var kind: StringName = KIND_IDLE
+## Toil-specific params — all values must be int, float, bool, String, Dict, or Array.
+var data: Dictionary = {}
+## Set by JobRunner when this toil is complete.
+var done: bool = false
+
+
+# ── factories ────────────────────────────────────────────────────────────────
+
+## Walk to the given tile. Stores coords as separate ints for JSON safety.
+static func walk_to(tile: Vector2i) -> Toil:
+	var t := Toil.new()
+	t.kind = KIND_WALK
+	t.data = {
+		"to_x": tile.x,
+		"to_y": tile.y,
+		"started": false,
+	}
+	return t
+
+
+## Pause for `n` sim ticks.
+static func wait_ticks(n: int) -> Toil:
+	var t := Toil.new()
+	t.kind = KIND_WAIT
+	t.data = {"ticks_remaining": n}
+	return t
+
+
+## Stand idle — never completes on its own; JobRunner must cancel or replace.
+static func idle() -> Toil:
+	var t := Toil.new()
+	t.kind = KIND_IDLE
+	t.data = {}
+	return t
+
+
+# ── save / load ──────────────────────────────────────────────────────────────
+
+func to_dict() -> Dictionary:
+	return {
+		"kind": str(kind),
+		"data": data.duplicate(true),
+		"done": done,
+	}
+
+
+static func from_dict(d: Dictionary) -> Toil:
+	var t := Toil.new()
+	t.kind = StringName(d.get("kind", str(KIND_IDLE)))
+	t.data = (d.get("data", {}) as Dictionary).duplicate(true)
+	t.done = d.get("done", false)
+	return t
+
+
+# ── convenience ──────────────────────────────────────────────────────────────
+
+## Rebuild Vector2i from the JSON-safe int fields. Only valid for KIND_WALK.
+func get_walk_destination() -> Vector2i:
+	return Vector2i(data.get("to_x", 0), data.get("to_y", 0))