docs(decisions): add D-031 time system, resolve Q-009

10 ticks = 1 game-minute, 4 day phases (Morning/Afternoon/Evening/Night),
diegetic time display on insert HUD. Unblocks daily routine pipeline (#88)
and all time-dependent systems. Workshop consensus from Tyre and Gestalt.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

DECISIONS.md

@@ -344,6 +344,19 @@ This document tracks confirmed decisions, open questions, and rejected alternati
 - **Raised by:** Tyre (architecture), Hoshe (testability analysis). Full workshop endorsed.
 - **Dissent:** GUT vs gdUnit4 resolved in Hoshe's favor — Tyre explicitly changed position. No remaining dissent.
 
+### D-031: Time system — game clock and day phases
+- **Date:** 2026-02-11
+- **Decision:** The v0.1 time system uses the following model:
+  - **Tick-to-time mapping:** 10 simulation ticks = 1 game-minute (at 10 tps, 1 real second = 1 game-minute). A 30-minute real-time play session covers ~12-18 game-hours — enough for a full NPC daily cycle.
+  - **Day phases:** Four phases drive routine transitions: Morning, Afternoon, Evening, Night. NPCs transition between routine activities at phase boundaries (e.g., go to work in Morning, to the bar in Evening).
+  - **Time display:** Diegetic — shown on the player's neural insert HUD. The character checks their insert to see the time, consistent with D-013.
+  - **Pause:** Available in single-player. Simulation freezes, UI stays responsive. Compatible with future multiplayer (D-009) where pause would be disabled or vote-based.
+  - **Time-skip:** Deferred for v0.1. The "wait/stake out" mechanic (if implemented) would advance time while the player observes from a fixed position.
+- **Not in scope for v0.1:** Deep time (years/decades), day/night lighting, seasonal cycles, time zones between locations.
+- **Resolves:** Q-009
+- **Raised by:** Tyre (technical proposal), Gestalt (day-phase design). Confirmed in Round 18 Gap Analysis Workshop with full team consensus.
+- **Dissent:** None.
+
 ### D-004: Team composition confirmed
 - **Date:** 2026-02-08
 - **Decision:** Team of 8 agents + Team Leader.
@@ -400,9 +413,7 @@ This document tracks confirmed decisions, open questions, and rejected alternati
 - **Assigned to:** Team Leader
 
 ### Q-009: Time system
-- **Status:** Not yet discussed
-- **Question:** How does time flow? Real-time with pause? Turn-based (days/weeks/months)? How do we handle deep time / decades passing?
-- **Assigned to:** Gestalt, Gore
+- **Status:** Resolved → D-031
 
 ### Q-010: Storyteller AI design
 - **Status:** Not yet discussed