docs(governance): D-226 amendment — agent-channel vocabulary reconciled to the stepped Atlas (T-971)

Tyre's PR #209 finding: every prior D-226 re-scope carries a dated
amendment in the record, and this vocabulary change existed only in
code comments and ticket appends. Records the drops (select_city,
open_regional — no settlement hit-test affordance post-D-255; one
screen Region..Chunk), the additions (open_atlas, jump_to_center via
the constrained jump_to seam), the summary-field reconciliation, and
the in-process-only transport narrowing.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

governance/decisions/architecture.md

@@ -1688,6 +1688,7 @@ Technical foundation decisions that constrain implementation: engine, client-ser
 - **Raised by:** Jeroen + Claude (design), with Tyre (channel/pause/headless architecture) + Araminta (overlay encoding + affordance UX), 2026-05-24.
 - **Cross-reference:** [D-225](#d-225) (layer-stream proxy — the data path), [D-166](#d-166) (per-layer Atlas progress viewer), [D-191](#d-191) (Atlas viewer), [D-169](#d-169) / [D-170](#d-170) (implant components / HUD occlusion — `gameplay_occluded` trigger), [D-200](#d-200) / [D-203](#d-203) (execution tiers / LRU cache), Q-099 (mod content catalog), `tests/run-visual` (capture primitive), `save_state.rs` (save-inspection consumer). **T-1112 amendment additionally:** [D-222](#d-222) (Quarter terminology — the 512m unit this layer surfaces), [D-234](#d-234) (footprint geometry — the block-subdivision source the aggregates summarize), [D-243](#d-243) (quarter = 512m rung, and the containment ladder that makes a quarter sub-pixel at planetary projection — Araminta's no-outline rationale), [D-010](#d-010) (determinism — integer-only aggregates, `BTreeMap` keying). **T-1124 amendment additionally:** [D-227](#d-227) (derive-don't-store + the "invented deterministically" clause this design is the first to surface on a screen; determinism is what makes the echoed-center staleness guard and the client-side window cache both sound), [D-243](#d-243) (district = 2,048m rung — this is precisely the D-226(d) ceiling's floor, the regional altitude above quarter-skeleton and below the never-mapped chunk/voxel tier; edge-fuzz discipline — the temperature quantization-consistency rationale), [D-239](#d-239) §6 (the frozen 17-zone `MorphologyZone` vocabulary this layer serves unchanged) / §8 (vegetation climate law, amended by T-1126's `Marine`), D-225 extension / T-1131 / PR #184 (the five-map-shape demux ceiling — why the window rides on `AtlasLayerRequest` rather than a new inbound shape), [D-010](#d-010) (wire-integer discipline — all six per-cell fields are integer/quantized, no `f32` on the wire). §5 (screen) additionally leans on [D-191](#d-191) (the `AtlasViewer` whose `_view_zoom` LOD vocabulary and `SETTLEMENT_LABEL_MIN_ZOOM` threshold the district window extends in place), [D-169](#d-169) / [D-170](#d-170) (implant chrome / theme accent-role discipline — map palettes stay out of `ACCENT_ACTIVE` gold the settlement marker owns), and [D-013](#d-013) (diegetic navigation — the zoom gesture owns spatial descent, so it is not overloaded onto the city-click sidebar). Tickets: T-1123 (the `derive_district` window-render precedent this design promotes to a served layer), T-1127 (glaciation_grade derivation + probe render pattern, wire half deferred here and now accepted), T-1126 (`VegetationClass::Marine`), T-1118 (region-grid climate overlay — §5's temperature/moisture overlays reuse its ramp so one colorizer spans both zoom levels), T-1119 (concurrent `quarter_footprints` wiring — the sibling whole-body layer this design's §2 distinguishes itself from).
 - **Dissent:** None
+- **Amendment (2026-07-25, T-971 / PR #209 — agent-channel vocabulary reconciled to the stepped Atlas):** the layer-4 `AtlasAgentInterface` ships with its intent vocabulary re-derived against the post-[D-255](#d-255) stepped Atlas, superseding this record's original list. **Dropped:** `select_city` and `open_regional` — post-D-255, settlements are `settlement_id` canvas cell values with no hit-test affordance (no server get-settlement-by-id, no client hit-test; a settlement-selection intent becomes its own ticket when a real consumer exists), and Region→Chunk is one screen (descent is `scroll_rung`, not a screen push — `open_body` replaces `open_regional`). **Added:** `open_atlas` (a driver must be able to start the session), and `jump_to_center` — the fixed-center revisit pattern proven by the T-1157 eyeball drivers, made first-class via `StepCanvasViewer.jump_to` (same request tail, extent cap, and cache keys as cursor navigation, so an agent cannot request a state a player couldn't). `get_layer_data_summary` reports the real `EncodedStepCanvas` fields (courses-by-class, cliffs, draw-matched settlement counts) — the original attractor/river/basin-count phrasing was retired-AtlasViewer vocabulary. **Transport narrowed:** in-process consumers only (gdUnit, `-s` drivers, the T-1157 capture harness — the committed reference driver replaces the scratch eyeball drivers); the original curl/terminal remote transport is a follow-up when a remote consumer exists. Full handler-by-handler mapping on T-971.
 
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