feat(content): D-084 dual-namespace line ID scheme — resolve Q-028 (#544)

Role namespace (shared pool) stays unchanged; instance namespace
(role-slug + seeded counter) added as opt-in for per-instance
authored content on auto-generated NPCs. No schema migration needed.

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

decisions/README.md

@@ -12,7 +12,7 @@ Cross-domain decisions live in one file with cross-reference notes in related fi
 |------|--------|-----------|
 | [architecture.md](architecture.md) | Technical foundation | D-008, D-009, D-010, D-012, D-020, D-026, D-030, D-031, D-041, D-042, D-054, D-055, D-066, D-068, D-073 |
 | [perception.md](perception.md) | Player observation | D-011, D-015, D-016, D-017, D-018, D-019, D-033, D-035, D-043, D-044, D-045, D-046, D-047, D-048, D-049, D-052, D-056, D-057, D-058, D-059, D-060, D-061, D-067, D-069, D-070, D-071, D-072, D-076, D-077, D-078 |
-| [content.md](content.md) | NPC, dialogue, templates | D-023, D-024, D-025, D-028, D-029, D-032, D-034, D-035, D-036, D-037, D-050, D-062, D-063, D-064, D-074 |
+| [content.md](content.md) | NPC, dialogue, templates | D-023, D-024, D-025, D-028, D-029, D-032, D-034, D-035, D-036, D-037, D-050, D-062, D-063, D-064, D-074, D-075, D-084 |
 | [scope.md](scope.md) | Game concept, prototype | D-001, D-003, D-005, D-006, D-007, D-013, D-014, D-027, D-038, D-039, D-051, D-053, D-065 |
 | [process.md](process.md) | Team, workflow | D-004, D-021, D-022, D-040 |
 | [questions.md](questions.md) | Open questions | Q-001 through Q-026 |

decisions/content.md

@@ -182,6 +182,28 @@ How narrative, NPCs, and world content are created: content tiers, NPC generatio
 - **Raised by:** Tyre (technical analysis, architecture synthesis)
 - **Dissent:** Gestalt endorses D-075 (reviewed 2026-02-19). The emergent archetype distinction is sufficient: access tier tags already encode "authority figure lines" vs "insider lines" in content; starting knowledge differentials produce different dialogue gate timings per character; adding an archetype filter would create per-character content maintenance burden and dilute the "two keyholes on the same world" experience (D-027). Knowledge vocabulary doc (#368) confirms this works in practice — same fact IDs, different starting confidence levels, different gate-open timing per character. *Nigel's input still pending.*
 
+### D-084: Dual-namespace line ID scheme — role pool + instance override
+- **Date:** 2026-02-25
+- **Decision:** Line IDs for auto-generated NPC content use a dual-namespace approach that eliminates the Q-028 collision problem without altering the existing ID format.
+  - **Role namespace (unchanged, primary):** `{role-slug}_{d|m|e}_{###}` — e.g., `dock-worker_d_001`. These are shared lines delivered by any instance of the role. One file, one ID sequence per role-at-location. No per-instance authoring, no collision possible. All existing authored content is unaffected.
+  - **Instance namespace (new, opt-in):** `{role-slug}-{zero-padded counter}_{d|m|e}_{###}` — e.g., `dock-worker-07_d_001`. Counter is the generation-order rank within the role group for that district, starting at 01, assigned deterministically from the world seed. Used only when a specific generated NPC needs authored content that differs from the role pool.
+- **Key design choices:**
+  - **Why the collision problem is mostly already solved:** The Q-028 collision framing assumed NPC-scoped IDs require per-instance ID sequences. They don't. D-028 tagged line pools are role-scoped: `dock-worker_d_001` is content that any dock worker can deliver. Forty dock workers all drawing from `dock-worker_d_###` is correct behavior, not a collision. A collision would only occur if two *distinct authored lines* shared the same ID — which the role namespace prevents by definition (one file, one sequence).
+  - **Instance namespace scope:** Opt-in only. Tier 3 (flat wallpaper) and Tier 2 (mundane triangles) auto-generated NPCs use the role pool exclusively. Instance pools are authored only when a specific generated NPC needs content variation the role pool cannot supply (e.g., a generated NPC flagged as a triangle member with unique tell lines).
+  - **History log disambiguation:** The speaker of a line is identified by `StableId`, not by line ID. Line ID identifies content; `StableId` identifies the speaker. `(StableId: 42, line_id: "dock-worker_d_001")` and `(StableId: 43, line_id: "dock-worker_d_001")` are two different log entries for the same content line — no collision in the log.
+  - **Counter stability:** Generation order within a role group is seeded from the world seed. Same seed → same order → same counter assignments. Counter is recorded in the district's NPC roster at world-gen time. The counter survives save/load because it is part of the generated NPC's profile, not recomputed at runtime.
+  - **Schema compatibility:** The existing ID regex `^[a-z][a-z0-9-]*_[dme]_\d{3}$` already accepts `dock-worker-07_d_001`. No regex change required. No content migration required.
+- **Rejected alternatives:**
+  - **StableId prefix (`npc-00042_d_001`):** StableId is assigned at load time from sorted canonical IDs. Authors cannot know it before writing files. A generate-then-bake pipeline would break the content/generation separation principle. Rejected.
+  - **UUID suffix (`dock-worker-a3f2_d_001`):** UUIDs are stable per seed but change across seeds, orphaning any authored instance content on replay. Rejected.
+  - **Slug registry with collision resolution (`dock-worker`, `dock-worker-2`, ...):** First instance gets a privileged non-suffixed slug while all others get a counter, creating asymmetry with no upside. Rejected.
+- **Implementation requirement:** The content registry (`server/src/knowledge/registry.rs` or a new `server/src/content/npc_slug.rs`) tracks a `RoleCounter: BTreeMap<String, u32>` per district. Incremented when a generated NPC claims an instance namespace slot. Stored in the district manifest. Provides `generate_instance_slug(role_slug) -> String` returning `{role-slug}-{counter:02}`.
+- **Hand-authored NPCs:** Unchanged. `kael-davan`, `sera-venn`, and all named authored NPCs keep their current slugs and ID sequences. No migration.
+- **Resolves:** Q-028
+- **Cross-reference:** Line ID scheme ([D-035](#d-035-converged-tag-taxonomy-for-dialogue-and-monologue-line-pools)), population model ([D-029](#d-029-population-entanglement-ratio--305020)), NPC generation ([D-024](#d-024-npc-generation-model--10-axes--combat-component))
+- **Raised by:** Gestalt (Sprint 18, #544). Endorsed by Tyre pending implementation review.
+- **Dissent:** None.
+
 ---
 
-*16 decisions. Last updated: 2026-02-19 (D-075 dissent updated)*
+*17 decisions. Last updated: 2026-02-25 (D-084 added — Q-028 resolution)*

decisions/questions.md

@@ -161,13 +161,13 @@ Tracked questions awaiting discussion or resolution.
 - **Source:** Sprint 10 PR review discussion (2026-02-19)
 
 ### Q-028: Collision-resistant line IDs for auto-generated NPCs
-- **Status:** Open
-- **Question:** The D-035 NPC-scoped line ID scheme uses NPC slugs as prefix (`kael-davan_d_001`). Hand-authored NPCs have unique slugs, but auto-generated populations (D-029: hundreds of NPCs) will produce collisions when the generator creates multiple NPCs with the same role slug (e.g., two `dock-worker` NPCs). What collision-resistance mechanism should be used? Options: (1) Short UUID/hash suffix on auto-gen slugs (`dock-worker-a7f3_d_001`), (2) Entity UUID as prefix, (3) Slug registry that guarantees uniqueness at generation time, (4) Composite key (entity ID + sequence) in server, human-readable slug only for authored content.
-- **Constraints:** Line IDs must be globally unique across entire save file lifetime (history log readiness). Must stay human-readable for hand-authored content. Server treats IDs as opaque strings — solution lives in content/generation layer. Must be compatible with D-035 NPC-scoped namespace.
+- **Status:** Resolved → [D-084](content.md#d-084-dual-namespace-line-id-scheme--role-pool--instance-override)
+- **Resolution:** The collision problem is mostly already solved by the role-pool architecture: `dock-worker_d_###` lines are shared content for all instances of the role, not per-instance IDs. A true collision (two distinct authored lines sharing the same ID) cannot occur with one file per role. For the edge case of authored instance-specific content, a role-slug + zero-padded generation counter suffix produces `dock-worker-07_d_001`. Counter is seeded-deterministic. No schema change, no migration. Hand-authored NPCs unchanged.
+- **Closed by:** Gestalt (Sprint 18, #544). 2026-02-25.
 - **Ticket:** #544
 - **Assigned to:** Gestalt, Tyre
 - **Source:** Sprint 16 PR #59 review discussion (2026-02-23)
 
 ---
 
-*28 questions (6 resolved, 1 partially resolved, 21 open). Last updated: 2026-02-24*
+*28 questions (7 resolved, 1 partially resolved, 20 open). Last updated: 2026-02-25 (Q-028 resolved → D-084)*