[EPIC][W4] The Living Stage — combat enters and exits IN PLACE; the full explore→talk→fight→loot loop

[100yenadmin]

Roadmap §4b/W4 (PR #1316). Depends: W1-W3; coordinate with S8 (demo assembly).

What

Combat becomes a MODE of the stage, not a separate screen: a fight starts from where everyone is standing and ends back at rest — plus day/night lighting live from the campaign clock.

Design (verified seams)

• start_combat (server.py:4039) gains an additive param seeding combatant cells from stage_cell (absent ⇒ today's spawn behavior). end_combat (server.py:6976) writes survivors' cells back to stage_cell. Gates-read-gauges holds: combat READS stage at entry, WRITES only at exit.
• Day/night: campaign clock × scene_grid.lighting (scene_grid.py:134) → additive surface lighting block; renderer re-tints (day plates exist, renderer: day-state plate selection (#1291) #1298 selection lands the engine-signal path via [engine] Surface campaign.time_of_day on /combat-surface (honest day/night signal) #1307).
• Combat grid and scene grid MUST be the same grid (dimensions/cells) — verify at seed time or the gate below fails by construction.

EVAL — the NO-TELEPORT gate

Scripted full loop (explore→talk→fight→loot→move-on): combat entry cells == last rest cells; exit cells == combat end cells; no actor jumps. Text-tier byte-identity.

Risks tracked

Mid-combat cross_door/travel (refuse or resolve — decide in-sprint with a test either way); foes lacking spawn keys (fallback cells).

ADDENDA — takeover review (2026-07-03, architect-ratified)

• [HIGH] Mid-combat cross_door/travel RULING: REFUSED while combat.active — the engine rejects with a clear error (mirroring existing combat-gated verbs); no mid-fight room transition in W4 scope. A fleeing-through-the-door mechanic is a future issue, not this epic.

• [HIGH] Grid-mismatch RULING: the start_combat stage-seeding param activates ONLY when the location's scene_grid dimensions match the combat grid (verify at seed time); on mismatch → today's spawn behavior (additive default), log a WARN-level line. Legacy campaigns therefore degrade gracefully.

• [HIGH] Foes lacking spawn placements: seed from the foes spawn bucket first, overflow per W1's ruling (zone_anchors id-sorted then party-adjacent vacant cells, round-robin) — never fail the combat start over placement.

• [MED] EVAL instrument named: (a) deterministic engine test — a scripted explore→start_combat→end_combat sequence asserting entry cells == prior stage_cells and exit cells == combat-end cells (the NO-TELEPORT gate, servers/engine/tests/); (b) ONE box render pair (rest frame + combat frame, same scene) as visual evidence. The blind-playtest loop eval belongs to W5, not W4.

• [HIGH] Depends on: [EPIC][W1] Scene at Rest — party + NPCs rendered in the room outside combat #1318 (stage_cell) + [EPIC][W2] Walk — within-room movement outside combat (walk_to + click-to-move + glide) #1319 (walk_to writes stage_cell)

  • [EPIC][W1] Scene at Rest — party + NPCs rendered in the room outside combat #1318
  • [EPIC][W2] Walk — within-room movement outside combat (walk_to + click-to-move + glide) #1319