docs: add Ash Underpass gameplay packet

ROADMAP.md

@@ -98,6 +98,9 @@ Recommended views:
   Underpass Signal`, the Tollkeeper Shell encounter, mission card, outcome
   report, dialogue flow, Body Hall, Gate HUD, offline-agent report, and
   reinhabitation presentation.
+- [x] Ash Underpass Gate gameplay packet documented for mission state,
+  room-by-room objectives, combat and objective authority boundaries, reward
+  outcomes, UI/audio needs, implementation packets, and evidence requirements.
 - [x] Alpha economy, balance, playtest, art, audio, and content direction
   documented for TIME, SECOND, reward defaults, reinhabitation pressure,
   playtest success metrics, visual tone, UI color language, audio placeholders,

docs/SUMMARY.md

@@ -19,6 +19,7 @@
 - [Alpha Level Design](design/27-alpha-level-design.md)
 - [Character, Body, and Roster Design](design/28-character-body-and-roster-design.md)
 - [Alpha Questline and Encounter Design](design/29-alpha-questline-and-encounter-design.md)
+- [Ash Underpass Gate Gameplay Design](design/54-ash-underpass-gate-gameplay-design.md)
 - [Alpha UX Flow](design/30-alpha-ux-flow.md)
 - [Alpha Economy, Balance, and Playtest Plan](design/31-alpha-economy-balance-and-playtest-plan.md)
 - [Alpha Art, Audio, and Content Direction](design/32-alpha-art-audio-and-content-direction.md)

docs/design/26-alpha-game-design-document.md

@@ -22,6 +22,9 @@ Companion execution docs:
 - [29-alpha-questline-and-encounter-design.md](29-alpha-questline-and-encounter-design.md)
   defines the first questline, encounter roles, Tollkeeper Shell, rewards, and
   failure states.
+- [54-ash-underpass-gate-gameplay-design.md](54-ash-underpass-gate-gameplay-design.md)
+  defines the first Gate mission's state machine, rooms, objectives, authority
+  boundaries, rewards, and evidence checklist.
 - [30-alpha-ux-flow.md](30-alpha-ux-flow.md) defines the first alpha UX flow
   from HUD to dialogue, Body Hall, Mission Board, outcome, agent report, and
   reinhabitation.

docs/design/27-alpha-level-design.md

@@ -26,6 +26,9 @@ Quest, encounter, and UX companions:
 - [29-alpha-questline-and-encounter-design.md](29-alpha-questline-and-encounter-design.md)
   defines the quest steps, enemy roles, Tollkeeper Shell, rewards, and failure
   states for this layout.
+- [54-ash-underpass-gate-gameplay-design.md](54-ash-underpass-gate-gameplay-design.md)
+  defines the detailed room contracts, objective state, encounter actors, and
+  evidence checklist for Ash Underpass.
 - [30-alpha-ux-flow.md](30-alpha-ux-flow.md) defines how the player reads the
   mission, Gate HUD, dialogue, outcome, and reinhabitation surfaces.
 

docs/design/29-alpha-questline-and-encounter-design.md

@@ -14,6 +14,12 @@ Gate encounter. It is intentionally small: one hub questline, one Gate mission,
 one elite or boss shell, one outcome report, and enough NPC context to make the
 world feel alive.
 
+Detailed Gate gameplay packet:
+
+- [54-ash-underpass-gate-gameplay-design.md](54-ash-underpass-gate-gameplay-design.md)
+  defines room contracts, mission state machine, objective validation,
+  encounter actors, outcome rules, and evidence requirements.
+
 Backlog coverage:
 
 - #33 Build first questline and hub NPC story beat.

docs/design/33-alpha-production-backlog.md

@@ -131,6 +131,12 @@ Goal:
 > Let the player choose a Gate mission with clear risk, reward, and body
 > suitability.
 
+Detailed build contract:
+
+- [54-ash-underpass-gate-gameplay-design.md](54-ash-underpass-gate-gameplay-design.md)
+  for the Ash Underpass mission definition, attempt lifecycle, state machine,
+  room flow, and evidence checklist.
+
 Required work:
 
 | Task | Acceptance |
@@ -153,6 +159,12 @@ Goal:
 > Prove the action loop with one short Gate route, one hostile type, one signal
 > objective, and one elite or boss shell.
 
+Detailed build contract:
+
+- [54-ash-underpass-gate-gameplay-design.md](54-ash-underpass-gate-gameplay-design.md)
+  for room contracts, encounter actors, combat/objective boundaries, and
+  partial/full clear rules.
+
 Required work:
 
 | Task | Acceptance |

docs/design/34-alpha-acceptance-matrix.md

@@ -11,6 +11,10 @@
 This document defines how to decide whether the alpha GDD has been implemented
 well enough to show to testers.
 
+Gate mission evidence should use
+[54-ash-underpass-gate-gameplay-design.md](54-ash-underpass-gate-gameplay-design.md)
+as the detailed room, state, objective, and outcome contract.
+
 It is intentionally practical. Each row maps a player-facing promise to:
 
 - required proof

docs/design/38-alpha-design-decision-register.md

@@ -141,6 +141,7 @@ When a design question appears during implementation:
 | `27-alpha-level-design.md` | The Garden and Ash Underpass blockout. |
 | `28-character-body-and-roster-design.md` | Body, roster, hostile body, voice, memory, and relationship rules. |
 | `29-alpha-questline-and-encounter-design.md` | First quest and encounter. |
+| `54-ash-underpass-gate-gameplay-design.md` | Detailed first Gate mission state, room, objective, and evidence contract. |
 | `30-alpha-ux-flow.md` | Player-facing UX flow. |
 | `31-alpha-economy-balance-and-playtest-plan.md` | TIME, SECOND, reward, playtest, and balance. |
 | `32-alpha-art-audio-and-content-direction.md` | Presentation, UI tone, audio, and content guardrails. |