context-system: bootstrap the progressive-context expert knowledge base (foundation)

Adapt the spark-lesson / expert-seed.md progressive-context pattern to the bt411 port:
a thin router + context/*.md knowledge graph so the 2236-line CLAUDE.md's deep knowledge
loads on-demand instead of every session.

NON-DESTRUCTIVE foundation pass (live CLAUDE.md unchanged; proposed router is a draft):
- reference/glossary.yaml        -- ~45 terms (engine/formats/scene/reconstruction)
- context/decomp-reference.md    -- the quantitative hub: resource types, ClassID map,
                                    mech offsets, damage delivery, weapon constants, env gates, tools
- context/reconstruction-gotchas.md -- the 12 systemic bug classes (conventions/DO-NOT hub)
- context/bgf-format.md          -- geometry format + CONN/PCONN + LOD-sqrt3 + ramp shading
- context/gauges-hud.md          -- the gauge/MFD system (the just-completed wave)
- context/open-questions.md      -- deferred systems + get-from-Nick
- context/_ROUTER-DRAFT.md       -- the proposed slim CLAUDE.md (identity, protocols,
                                    quick-lookup, evidence tiers T0-T4, conventions, structure)
- phases/phase-01-context-restructure.md -- design + migration plan + status

docs/*.md ledgers stay as the DETAILED logs; context/*.md are the curated digests that
route into them. Remaining: ~10 topic files (project-overview, subsystems, combat-damage,
rendering, locomotion, wintesla-port, build-and-run, ...) then the CLAUDE.md swap.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

phases/phase-01-context-restructure.md

@@ -0,0 +1,60 @@
+# Phase 01 — Progressive Context Restructure
+
+**Goal:** adapt the `spark-lesson`/`expert-seed.md` progressive-context pattern to the bt411
+port, turning the 2236-line monolithic `CLAUDE.md` into a thin router + a `context/*.md`
+knowledge graph. Motivation: CLAUDE.md is loaded every session and is too large; the deep RE
+knowledge should load on-demand.
+
+## Design decisions
+- **In-place** (context/ + reference/ at bt411 root, mirroring spark-lesson), NOT a separate repo.
+- The router serves DOUBLE duty: expert-agent knowledge routing AND the load-bearing WORK
+  directives (build recipe, "keep current" mandate) — bt411's CLAUDE.md drives active work, unlike
+  spark-lesson's pure knowledge base.
+- The existing **`docs/*.md` ledgers stay** as the DETAILED running logs (RECONCILE 1555 lines,
+  GAUGE_COMPOSITE 627, HARD_PROBLEMS, SUBSYS_PLAN, P3_LOCOMOTION, …). The `context/*.md` files are
+  the CURATED digests that route into them. (docs/ ≈ spark-lesson's phases/; context/ ≈ its context/.)
+- **Evidence tiers adapted for RE:** T0 engine/header truth · T1 decompiled+verified · T2
+  reconstructed+runtime-verified · T3 best-effort/guarded · T4 unconfirmed hypothesis.
+- **Non-destructive:** the live `CLAUDE.md` is UNCHANGED until the migration is complete + approved.
+  The proposed router is `context/_ROUTER-DRAFT.md`.
+
+## Status
+
+### ✅ Foundation built (this pass)
+- `reference/glossary.yaml` — ~45 terms (platform/engine, formats, scene/entity, reconstruction).
+- `context/decomp-reference.md` — the quantitative hub: resource-type enum, ClassID map, mech
+  offsets, damage delivery, weapon constants, env gates, tools.
+- `context/reconstruction-gotchas.md` — the 12 systemic bug classes (the conventions/DO-NOT hub).
+- `context/bgf-format.md` — geometry format + CONN/PCONN + LOD √3 + ramp shading (frames docs/BGF_FORMAT.md).
+- `context/gauges-hud.md` — the gauge/MFD system (frames docs/GAUGE_COMPOSITE.md); the just-completed wave.
+- `context/open-questions.md` — deferred systems + get-from-Nick.
+- `context/_ROUTER-DRAFT.md` — the proposed slim CLAUDE.md (identity, protocols, quick-lookup,
+  evidence tiers, conventions, structure).
+
+### ☐ Remaining topic files (the next tranche — migrate from CLAUDE.md §/docs)
+| topic | source in CLAUDE.md / docs |
+|---|---|
+| `project-overview.md` | §1-3 |
+| `pod-hardware.md` | §3 |
+| `content-archives.md` | §4, §4a |
+| `asset-formats.md` | §5, docs/ASSET_PIPELINE.md |
+| `source-completeness.md` | §5a, docs/BT_SOURCE_STATUS.md |
+| `wintesla-port.md` | §5b, §8 |
+| `build-and-run.md` | §10a, §10a-bis |
+| `reconstruction-method.md` | §10b |
+| `locomotion.md` | §7, docs/P3_LOCOMOTION.md |
+| `subsystems.md` | §10d, docs/SUBSYS_PLAN.md, docs/VEHICLE_SUBSYSTEMS.md |
+| `combat-damage.md` | §10c, docs/HARD_PROBLEMS.md |
+| `rendering.md` | §10 render-fidelity notes (large) |
+| `multiplayer.md` | §7 Phase 7, §8 P6 |
+
+### ☐ Swap (after review + full migration)
+1. Move the current `CLAUDE.md` deep content into the topic files above.
+2. Replace `CLAUDE.md` with `context/_ROUTER-DRAFT.md` content (preserving the git history of the old).
+3. Verify: a fresh session reads the router → quick-lookup → topic files load on demand.
+
+## Notes
+- The router keeps the build one-liners + the "keep current" mandate so active port work is
+  uninterrupted. The detailed §10 combat-bring-up narrative migrates to `combat-damage.md` +
+  `locomotion.md` + `rendering.md` + the docs/ ledgers it already references.
+- Cross-references use `[[topic-id]]`; the glossary uses `related_topics`.