coc-chase

name

coc-chase

description

Resolve Call of Cthulhu chase scenes during COC mode using the full Chapter 7 Parts 1-5 system. Use for establishing pursuits (CON/Drive Auto speed rolls), Cut to the Chase positioning, location chains with hazards and barriers, movement-action economy, Pedal to the Metal, passenger assists, firing while moving, Choosing a Route, Sudden Hazards, same-location melee delegated to CombatSession, vehicle Drive Auto conflict, and structured chase state persistence via ChaseSession and save/chase.json.

COC Chase

A chase is not a single speed contest. Per Keeper Rulebook Chapter 7 (p.130-145), play runs through five parts: establish whether a chase is needed, cut to the exciting range, resolve movement through hazards and barriers, handle same-location conflict, then optionally embellish with Part 5 rules. Every chase scene drives a ChaseSession (../../scripts/coc_chase.py) that owns positions and the location chain, and persists save/chase.json.

Boundary: chase owns positions / movement economy / location chain. Same-location melee delegates to CombatSession (../../scripts/coc_combat.py) — combat owns the exchange. Do not invent a second combat resolver inside chase.

Part 1 — Establishing the Chase (p.132)

1. Construct ChaseSession(chase_id, rng=...).
2. add_participant for each pursuer and quarry (foot: con=; vehicle: is_vehicle=True, drive_auto=, build=). Use get_vehicle_stats("car_economy") etc. for Table V defaults.
3. Call establish():
   • Success → MOV unchanged; Extreme → +1 MOV; Failure → −1 MOV (whole chase).
   • If every quarry's adjusted MOV is higher than every pursuer's → conclude("escaped") and narrate; do not play Parts 2-4.
4. Passengers: add_passenger(actor_id, vehicle_id, dex=...) — no speed roll, no movement actions (p.142).

Part 2 — Cut to the Chase (p.132-133)

cut_to_the_chase(gap=2, location_count=8)
# or cut_to_the_chase(gap=2, locations=[...structured entries...])

• Default gap is 2 locations (pursuers at 0, quarry at 2). Gap 1 only for exceptional tension; do not exceed 2.
• Each location entry is structured: {label, hazard, barrier} — hazard/barrier slots may be null until filled.
• generate_location_chain(count) builds an empty structured chain when the Keeper has not authored one.

Part 3 — Movement, Hazards, Barriers (p.134-137)

Movement actions

begin_round() recomputes actions: 1 + (MOV − slowest), then subtracts any movement_debt from a prior failed hazard. Participants act in DEX order (rounds[].dex_order).

Clear advance

move_participant(actor_id, [{"type": "advance"}])

Cost: 1 movement action per location when the edge is clear.

Hazards (p.134-135)

Hazards sit on the location being entered. An advance into a hazarded location rolls the Keeper-chosen skill:

• Cautious approach: cautious_bonus_actions 1 or 2 → that many bonus dice (max 2), each costing an extra movement action.
• Success: advance; no further delay or damage.
• Failure: damage (Table III / Table VI) and 1D3 movement-action debt, but still advance (p.135).

Debt reduces next round's movement actions via begin_round.

Barriers (p.136-137)

Barriers block until negotiated or destroyed. Simple advance returns blocked_by_barrier.

Action	API	Rule
Skill past	{"type":"barrier","skill":"Climb","target":40}	Fail → stay put
Smash	{"type":"break_barrier"}	Build×1D10 (no attack roll). Vehicle that fails to destroy → wrecked; wreck becomes a hazard. Destroyed barrier → debris hazard; vehicle takes half barrier HP prior to impact

Sample barrier HP (p.137): thin fence 5, back door 10, strong door 15, 9″ brick 25, tree 50, concrete support 100.

Part 4 — Conflict (p.137-138)

Characters/vehicles must share a location (except firearms). Initiating an attack costs 1 movement action.

Same-location melee → CombatSession

combat = CombatSession(...)
chase.initiate_melee_conflict(
    attacker_id, defender_id,
    combat_session=combat,
    declared_intent="grab the farmer",
    defense_kind="dodge",
)

Chase spends the movement action and keeps positions; declare_and_resolve_turn resolves the exchange. HP syncs back onto chase participants.

Vehicle vs vehicle

chase.vehicle_conflict(attacker_id, defender_id, defense_kind="dodge")

Opposed Drive Auto (Fighting/Dodge substitute). Damage = winner's Build×1D10; striker takes half (capped by target's Build). Build drops 1 per full 10 HP (p.145). Build difference applies penalty dice (1 / 2 / impossible at +3).

Collisions

apply_vehicle_collision(actor_id, severity="moderate") wires Table VI into the session (build damage, passenger HP, movement debt) and records pending rolls/events.

Part 5 — Optional rules (priority order)

1. Pedal to the Metal (p.139-140)

{"type": "pedal_to_the_metal", "locations": 3, "skill": "Drive Auto", "target": 60}

One action moves 2–5 locations. Hazards take 1 penalty die (2–3 locs) or 2 (4–5). Commitment cannot be retracted; stop on a failed hazard.

2. Passenger actions (p.142)

passenger_action("nav", {"type": "assist_driver", "skill": "Spot Hidden", "target": 70})

Success → vehicle gains assist_penalty_reduction (−1 penalty die on next Pedal move). Passengers may also {"type":"fire", ...}.

3. Firing while moving (p.142)

fire_while_moving(attacker_id, target_id, firearms_target=50, moving=True)

• Moving: +1 penalty die, 0 movement-action cost.
• Stopped: 1 movement action, no movement made, no extra penalty.
• Occupants gain vehicle armor from Table V.

4. Choosing a Route (p.139)

choose_route(quarry_id, alternate_locations=[...])

Preserves locations at/behind the quarry; replaces the upcoming chain (e.g. river path with a Swim hazard).

5. Sudden Hazards (p.139)

sudden_hazard(caller="players", luck_target=50)
sudden_hazard(caller="keeper", luck_target=50)  # must alternate

Luck success → caller places a Regular hazard; failure → the other side places. Callers must alternate.

roll_random_hazard(environment="normal"|"hazardous"|"safe") implements the 01–59 clear / 60+ Regular / 85+ Hard / 96+ Extreme table.

Persistence

• save(campaign_dir) → atomic save/chase.json via write_json_atomic.
• ChaseSession.load(path, rng=...) restores participants, chain, rounds, and sudden-hazard alternation state.
• Drain drain_pending() / drain_events() into campaign roll/event logs after each turn.
• Audit reads save/chase.json — never trust transcript prose for chase mechanics.

Table V vehicles (p.145)

Key	MOV	Build	Armor	Passengers
car_economy	13	4	1	3–4
car_standard	14	5	2	4
car_deluxe	15	6	2	4
sports_car	16	5	2	1
pickup_truck	14	6	2	2+
truck_6_ton	13	7	2	2+
motorcycle_light	13	1	0	1
motorcycle_heavy	16	3	0	1

Aliases: motorcycle → light; truck → 6-ton. Data lives in references/rules-json/chase.json.

Workflow checklist

1. Create/load ChaseSession → save/chase.json.
2. Add participants (and passengers); establish().
3. If chase proceeds: cut_to_the_chase(gap=2, ...).
4. Each round: begin_round → DEX order → move_participant / conflict / optional Part 5 APIs.
5. check_outcome() / conclude(...) when quarry escapes or is captured.
6. Return to immersive play; keep mechanical truth in the JSON snapshot.

Use [meta] for detailed rule explanation when the player asks. Keep this skill host-neutral — no Codex-only or Cursor-only gates.