docs: fill RQ2-P3 half of combined companion paper from sealed record

Post-seal, un-blinded fill of the RQ2-P3 mechanism track in the combined
companion paper (D3), matching the lead paper's post-seal discipline. RQ3
remains fully HELD-BLIND (battery still running; progress read by sidecar
count only).

- §3: FREEZE-PENDING -> FROZEN 2026-07-21 (prereg SHA 8db4e8a7...)
- §5 Results (RQ2-P3): H1 rho=+0.6244 CI[+0.5941,+0.6545]; H2 slope=+0.7052
  CI[+0.6195,+0.7903] (n=270, run-level cluster bootstrap); H3 RESOLVED=MIX;
  Holm own {H1,H2} both reject. Effect+CI, never bare p.
- §6 Discussion: shared-pool concentration RAISES anonymity (mix), refuting
  the naive funnel; honest qualification/correction of the lead RQ2-P1
  "shrink" as a unique-bridge (fresh-bridge-per-circuit) artifact, per
  note-unique-bridge-artifact.md + frozen mechanism prereg. Mandatory
  disclosure: §7 dry-pass previewed direction (rho 0->+0.838); hypotheses
  were pre-committed two-sided.

RQ3 Results/Discussion and the authoritative Holm-7 stay HELD-BLIND until
rq3-battery-results.json lands. Lead RQ2-P1 + frozen lead prereg untouched.

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

docs/stage-07-companion-methods.md

@@ -9,10 +9,13 @@
 > written as **self-contained sections** that can be lifted into either structure.
 >
 > **Blinding & gating status (binding).**
-> - **RQ2-P3 mechanism study** — the prereg (`docs/rq2p3-mechanism-prereg.md`, own slug
->   `sor-consent-rq2p3`) is **NOT YET FROZEN** (§10 empty). Its methods section below is marked
->   **FREEZE-PENDING**; **no confirmatory cell** runs until the operator records the SHA-256 in
->   §10 and signs off.
+> - **RQ2-P3 mechanism study — FROZEN + SEALED; its Results/Discussion are now UN-BLINDED below.**
+>   The prereg (`docs/rq2p3-mechanism-prereg.md`, own slug `sor-consent-rq2p3`) was **frozen
+>   2026-07-21** (§10 signed; full-file SHA-256 `8db4e8a7ac60f8b2861f2387249db68a3fd44822f6b3d9c7c6990ff65f261a3b`
+>   in the sidecar `docs/rq2p3-mechanism-prereg.sha256`). The confirmatory battery then ran
+>   **offline + deterministic** and its record is **sealed** (`output/sor-rq2p3-confirmatory/…`,
+>   results SHA-256 `5fdcb379d8a2…`). §5/§6 for RQ2-P3 are filled **from that sealed record only**,
+>   the same post-seal discipline the lead paper used.
 > - **RQ3 companion** — hypotheses, gates, and analysis are **already frozen** in the lead prereg
 >   (`sor-consent-prereg.md`, SHA-256
 >   `f22331a72e0d0ccf38b787e63acabbe9d666456ec76076787a6d545c3193425b`, §3/§4/§6); the two open
@@ -99,13 +102,15 @@ references:
 
 ---
 
-## 3. Methods A — RQ2-P3′ funnelling-mechanism study **[FREEZE-PENDING (prereg §10 not yet signed)]**
+## 3. Methods A — RQ2-P3′ funnelling-mechanism study **[FROZEN 2026-07-21 — prereg §10 signed]**
 
-> **This section describes a study whose prereg (`docs/rq2p3-mechanism-prereg.md`) is NOT frozen.**
-> Design and parameters are operator-approved and locked; the **human freeze checkpoint** (SHA-256
-> in §10 + sign-off) is outstanding. No confirmatory cell is run until then. Everything below is
-> the pre-registered *plan*; the calibration numbers cited are the pre-registered §7 gate output,
-> explicitly **not** confirmatory results.
+> **This section describes a study whose prereg (`docs/rq2p3-mechanism-prereg.md`) is FROZEN.**
+> Design and parameters were operator-approved and locked; the **human freeze checkpoint** (§10
+> signed 2026-07-21, full-file SHA-256 `8db4e8a7ac60f8b2861f2387249db68a3fd44822f6b3d9c7c6990ff65f261a3b`
+> in the sidecar `docs/rq2p3-mechanism-prereg.sha256`) is complete. The confirmatory battery then
+> ran **offline + deterministic** and its record is **sealed** (results SHA-256 `5fdcb379d8a2…`).
+> Everything below is the pre-registered *plan* exactly as frozen; the §5/§6 numbers are read
+> **from that sealed record only**.
 
 **Design (manipulated-IV dose-response).** A new assembler topology, `bridge-federated-pool`,
 replaces the fresh-per-seed bridge with a **finite willing-bridge pool** of size `B` under a fixed
@@ -236,10 +241,21 @@ confirmatory battery and have both passed on a **dry, synthetic, offline** pass:
 
 ## 5. Results *(HELD-BLIND — no confirmatory number written)*
 
-- **RQ2-P3′ (H1 / H2 / H3).** *HELD — pending prereg freeze (§10) and the confirmatory run.* No
-  Spearman ρ, OLS slope, CI, or Holm decision is computed or inspected until after freeze. *(The
-  only figures on record are the §4/§3-A pre-registered **calibration** preview — ρ 0→+0.838, B=1
-  high-H — explicitly labelled calibration, not a result.)*
+- **RQ2-P3′ (H1 / H2 / H3) — RESOLVED: MIX.** From the sealed confirmatory record (9 cells × R=30 ×
+  C=50, offline + deterministic, S0 = 20260719):
+  - **H1 (within-cell association).** Pooled Spearman **ρ = +0.6244**, BCa 95% CI **[+0.5941, +0.6545]**
+    (run-level cluster bootstrap, 10,000 resamples). CI excludes 0 on the **positive** side → **mix**.
+  - **H2 (dose-response).** OLS slope of per-run mean-H on per-run mean concentration
+    **β = +0.7052**, BCa 95% CI **[+0.6195, +0.7903]** over n = 270 run-level points. CI positive →
+    **mix**.
+  - **H3 (joint).** H1 and H2 **agree in sign (both +)** and **both exclude 0** → mechanism
+    **RESOLVED = MIX**.
+  - **Holm (own family {H1-pooled, H2-slope}, size 2).** Both tests **reject** at α = 0.05 after
+    Holm correction. *(p carried only for Holm ordering; the effect + CI above are the reported
+    quantities — never a bare p.)*
+  - Across the sweep, as pool size B rises concentration falls **and** entropy H falls together
+    (e.g. B=2/α=0: conc ≈ 1.00, H ≈ 2.54; B=8/α=0: conc ≈ 0.51, H ≈ 2.19) — concentration and H move
+    **together, positively**: higher concentration ⇒ higher anonymity (mix), not lower (funnel).
 - **RQ3-P1-perf / RQ3-P1-latency / RQ3-P2 / RQ3-P3.** *HELD — pending operator-GO on the live
   isolated grid.* Throughput-retention margin, added-latency (live-only), and rebuild-classifier
   AUC over confirmatory cells are **not** computed; the only figures on record are the two green
@@ -248,10 +264,26 @@ confirmatory battery and have both passed on a **dry, synthetic, offline** pass:
 
 ## 6. Discussion *(HELD-BLIND — placeholders)*
 
-- **Does a shared bridge funnel or mix?** *HELD.* If H1/H2 confirm **mix** (ρ, slope > 0), the
-  companion qualifies the lead "shrink" as partly a unique-bridge artifact; if **funnel** (< 0), the
-  lead reading is mechanistically corroborated; if inconclusive, the mechanism stays open. The sign
-  is the finding; the lead RQ2-P1 result is reported as-is and not re-litigated.
+- **Does a shared bridge funnel or mix? — It mixes.** Both pre-registered two-sided tests resolve
+  **positive** (H1 ρ = +0.6244 CI [+0.5941, +0.6545]; H2 β = +0.7052 CI [+0.6195, +0.7903]; H3
+  RESOLVED = mix; Holm both reject). Plainly: **concentrating circuits through a finite shared
+  willing-bridge pool RAISES the per-circuit anonymity set** — circuits that share a bridge share an
+  exit signature, so the observation-consistent set grows and entropy rises. This **refutes the naive
+  funnel intuition** (that concentration would shrink the set) and, per the mechanism developed in
+  `docs/note-unique-bridge-artifact.md`, **qualifies the lead RQ2-P1 "shrink" as a unique-bridge
+  (fresh-bridge-per-circuit) instrument artifact**: the lead topology assigned a *fresh* bridge per
+  circuit seed, making every exit signature unique, every anonymity set size 1, and H≈0 by injective
+  construction rather than by funnelling. Under a finite shared pool the injectivity is removed and
+  the true sign of the concentration→anonymity relationship is revealed to be a **mix**. This is an
+  honest **qualification/correction** of the lead reading via the frozen mechanism prereg (SHA-256
+  `8db4e8a7ac60f8b2861f2387249db68a3fd44822f6b3d9c7c6990ff65f261a3b`), **not** an overwrite: the lead
+  RQ2-P1 result and its frozen prereg stand as published and are not re-litigated.
+  - **Mandatory disclosure (pre-registration honesty).** The §7 calibration dry-pass — synthetic,
+    offline, no confirmatory record read — **already previewed this direction** (Spearman ρ running
+    0 → +0.838 across the sweep, B=1 boundary at high entropy). The confirmatory battery therefore
+    **quantifies a dose-response that was already visible at calibration**; the pre-committed
+    hypotheses were nonetheless **two-sided** and that pre-commitment is unchanged. We surface the
+    calibration preview openly so no reader mistakes the confirmatory sign for a post-hoc choice.
 - **Does the agent selector help without leaking?** *HELD.* RQ3-P3 confirms only if the agent both
   clears the +10 pp retention / ≤100 ms latency bar **and** leaves a non-classifiable rebuild
   pattern (AUC CI upper ≤ 0.60); either failure is an honest H0 (perf cancelled by teardown