diff --git a/specs/STATE.md b/specs/STATE.md
index cc990dc..c2fdc2b 100644
--- a/specs/STATE.md
+++ b/specs/STATE.md
@@ -1,5 +1,5 @@
 # VYNDR — STATE OF THE WORLD
-### As of `927e867` (main, DEPLOYED), 2026-07-21. This file opens every future session. **Start with the CURRENT STATUS + OPEN ITEMS block below.**
+### As of `3ac91c3` (main, DEPLOYED), 2026-07-21. This file opens every future session. **Start with the CURRENT STATUS + OPEN ITEMS block below.**
 
 ---
 
@@ -131,6 +131,80 @@ exist locally; harmless, the data restores completely.
 `specs/snapshot-retention.md` (Phase 2 report + schema) ·
 `specs/audit-data/grade-collapse.md` · `specs/audit-data/gate-simulation.md`.
 
+---
+
+# 🟡 SESSION 73 — PARK FACTORS (derived, composable) (2026-07-21)
+**Derivation + composition BUILT and proven. PIPELINE WIRING INCOMPLETE — see
+the gap.** Layer 3 Step 4.
+
+## 🔴 PHASE 0 — A STATIC PARK TABLE ALREADY EXISTED (nearly built a duplicate)
+`src/data/parkFactors.js` — **static FanGraphs table, Session 15**, consumed by
+`computeFeatures.js:374`. I almost created a second source of truth.
+- **NEW derived service = `src/services/parkFactors.js`** (distinct path).
+- **Checked:** the static table reaches `computeFeatures` but **NOT
+  `probabilityEstimator`** → it does **not** currently touch `p_win`.
+- **This reframes the order:** if the champion ever does see park, adding it to
+  the challenger is DOUBLE-COUNTING — precisely what the S72 harness catches.
+  Park therefore ships as a **nominated challenger to be TESTED**, not an
+  assumed win.
+
+## Derivation (ours, from real games)
+statsapi `schedule?hydrate=linescore,venue,scoringplays` — **one call per date
+range**. Every HR scores ≥ the batter, so **HR totals are fully recoverable from
+scoringPlays**. Derived from **5,055 real games, 2022–2025**:
+
+| Park | HR base | RUN base |
+|---|---|---|
+| Dodger Stadium | **1.106** | 1.023 |
+| Coors Field | 1.029 | **1.099** |
+| Oracle Park | **0.923** | 0.969 |
+| PNC Park | **0.917** | 0.994 |
+
+**18 parks present · 18 honestly absent** (below the 150-game regime floor).
+*(Sample was a partial pull — month-chunked with `-31` end dates drops days — so
+absences are inflated. Re-derive with proper date ranges before trusting counts.)*
+
+## COMPOSABLE — the architectural point
+Emits a **multiplier ~1.0**, never an additive nudge, because weather must
+modulate it next: `effective = park_base × weather_mod × …`. Additive terms
+don't compose (5% park + 8% wind = 1.05×1.08, **not** +13%). The challenger
+converts via `Math.log(env)` into the same log-odds space the archetype nudges
+use. A test multiplies a placeholder weather term on to prove the shape composes
+**with no rearchitecting**.
+
+## Honest states (three, distinct)
+`absent` (thin → adjust nothing) · `present` (adjust) · **`weather_na`** (dome —
+**the park factor STILL APPLIES**; the flag exists so next order's weather does
+nothing there). **N/A ≠ absent** — conflating them either drops a valid park
+factor or applies wind indoors.
+
+## Directional by prop-owner
+`home_runs` and `home_runs_allowed` both key off `hr_base` **in the same
+direction** — the sign lives in the STAT, not the park.
+
+## Structural breaks + shrinkage
+A deviating season starts a new regime **only if the NEXT season confirms** (one
+odd year = noise). Only post-break seasons used. Factors **regress toward
+neutral by sample size**; fine conditioning (park×hand, park×batted-ball) stays
+**unavailable** until its own larger floor (400 games).
+
+## 🔴 THE GAP — park is NOT yet reaching live props
+`adjust()` accepts `environment`, and `parkMultiplier` produces it — but
+**nothing in `snapshotService` looks up a venue per prop and passes it**. Props
+carry `game_time` (via gameBinder) but **no venue**. Remaining wire-up:
+1. Attach venue to each prop (statsapi schedule already returns it).
+2. Persist derived factors (a table or cached blob) + a refresh job.
+3. Pass `environment` into `attachChallenger`.
+**Until then park adjusts nothing live** — the derivation and composition are
+proven, the plumbing is not.
+
+## Next
+1. Wire venue → prop → park lookup (the gap above).
+2. **Weather modulation** — composes by multiplying `park_base`; domes already
+   flagged `weather_na`.
+3. Still blocking all measurement: **no settled row carries `p_win` yet**.
+
+
 ---
 
 # 🟢 SESSION 72 — TIER-1 MAPPINGS LIVE + TIER-2 HARNESS (2026-07-21)