diff --git a/CHANGELOG.md b/CHANGELOG.md
index 70e7929..624d304 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -12,6 +12,7 @@ Format follows [Keep a Changelog](https://keepachangelog.com/en/1.1.0/).
 - **Compliance cost model verified — SOC 2 readiness is ~$15–17K first-year, not $20–50K.** The compliance-readiness tracker's cost table is filled from real quotes (2026-08-07 compliance-automation platform conversation): ~$12K/yr platform covering both SOC 2 and ISO 42001, ~$3K Type I, ~$4–5K Type II, pen test and ISO 42001 bundled at no increment. Cost is no longer the gating variable — the trigger remains the first enterprise contract requiring certification. The three-horizon map's P5 profile carries the same economics. Numbers rounded and vendor-neutral in the public tree; attributed quote record internal. Docs only — no product impact. (#454)
 
 ### Added
+- **Guinea-pig port verified: cpex-ocsf-audit runs clean against the cpex#166 audit seam.** Delivers the commitment made on the cpex PR thread (2026-08-14): the OCSF audit plugin built and ran its full suite (21/21 tests, `cargo check --all-targets` clean) against `feat/audit-seam` @ `386710a` — the post-hardening head — with zero source changes, confirming the seam's "all changes are opt-in" claim for a real out-of-tree consumer. `integrations/cpex-ocsf-audit/SEAM-PORT-RESULTS.md` records scope (the `AuditHandler`/`DecisionLog` sink port with the `DenyIgnored`/`Aborted` mapping remains the tracked WS-A/P1 next step), findings for upstream (cpex-core gains `futures` + `sha2` transitive deps; the 1.96 MSRV pin fails fast), and repro steps; the committed `Cargo.lock` pins the exact resolution used. Docs/test evidence only — no product impact. (#456)
 - **Full agent test suite now runs in CI on `agent/**` changes.** The Ada Evals workflow ran only the static citation gate (deliberately no ADK install), so the other ~150 agent tests ran nowhere — how a test sat red on `main` for weeks after #235 and how the ADK 0.4→2.7 drift stayed invisible until #452. New `agent-tests` job installs from the exact-pinned `agent/requirements.txt` on Python 3.13 and runs the whole suite; separate job keeps the citation gate fast, the existing path filter keeps main CI untouched for non-agent changes, and it is deliberately not a required check (path-filtered required checks block merges when skipped). CI only — no product impact. (#453)
 
 ### Fixed
diff --git a/integrations/cpex-ocsf-audit/Cargo.lock b/integrations/cpex-ocsf-audit/Cargo.lock
index dc7ef1e..7a6f61b 100644
--- a/integrations/cpex-ocsf-audit/Cargo.lock
+++ b/integrations/cpex-ocsf-audit/Cargo.lock
@@ -132,10 +132,12 @@ dependencies = [
  "async-trait",
  "chrono",
  "cpex-orchestration",
+ "futures",
  "hashbrown",
  "serde",
  "serde_json",
  "serde_yaml",
+ "sha2",
  "thiserror",
  "tokio",
  "tokio-util",
diff --git a/integrations/cpex-ocsf-audit/SEAM-PORT-RESULTS.md b/integrations/cpex-ocsf-audit/SEAM-PORT-RESULTS.md
new file mode 100644
index 0000000..76c2a8a
--- /dev/null
+++ b/integrations/cpex-ocsf-audit/SEAM-PORT-RESULTS.md
@@ -0,0 +1,69 @@
+# Guinea-pig port results — cpex-ocsf-audit vs. the audit seam (cpex PR #166)
+
+**Date:** 2026-08-18
+**Plugin:** `cpex-plugin-ocsf-audit` v0.0.3 (this directory, unmodified)
+**Against:** `contextforge-org/cpex` branch `feat/audit-seam`, PR #166 head
+`386710a` (includes the 2026-08-18 hardening round `eda9821`, the h2 bump
+`1660773`, and the clock-assumptions doc `82b92c3`)
+**Toolchain:** rustc 1.96.1 (the repo's `rust-toolchain.toml` pin / MSRV)
+
+This is the follow-through on the offer made on the PR thread (2026-08-14):
+be the first outside consumer to port against the seam and report anything
+that doesn't match intent.
+
+## Results
+
+| Check | Result |
+|---|---|
+| `cargo check --all-targets` (lib, tests, examples) | **Clean** — no errors, no warnings |
+| `cargo test` | **21 passed, 0 failed** (emitter 14, sign 7, doc-tests 0) |
+
+The plugin required **zero source changes** to build and pass its full suite
+against the seam branch. Every behavior we assert — OCSF 6003 shaping,
+`ai_operation` mapping, readOnlyHint→activity derivation, fingerprint
+chaining/predecessor binding, JCS canonicalization, DSSE signing and offline
+verification, observation-only handler contract — is intact.
+
+## What this does and does not verify
+
+**Verified:** the seam is additive for an existing CMF post-hook observer.
+The PR's claim that "all changes are opt-in; no behavior changes without
+explicit configuration" holds for a real out-of-tree consumer, not just the
+in-tree `audit-logger`.
+
+**Not yet exercised (next step of the port):** registering as a
+decision-audit sink (`AuditHandler` / `DecisionLog`) and mapping the
+finalized decision vocabulary — `Allowed` / `ModifiedPayload` /
+`ModifiedExtensions` / `DenyIgnored` / `Aborted` / `Error`, terminal
+verdicts, `plugin_panic` coding, and the `(epoch, stream_seq, emission_seq)`
+stamps — into OCSF records (deny/modify records, action_id 2/4). That is the
+WS-A / P1 work item already tracked in `src/lib.rs`; the vocabulary review
+on the PR thread (2026-08-18) confirmed the contract carries everything the
+mapping needs.
+
+## Observations for upstream (the "anything that doesn't match intent" list)
+
+1. **Nothing broke.** No API drift against `cpex-core` 0.2.2 on the seam
+   branch; the port was a lockfile refresh, not a code change.
+2. **New transitive dependencies:** `cpex-core` now pulls `futures` (serial
+   panic containment via `catch_unwind`) and `sha2` (content provenance
+   hashing). Both small and justified; embedders doing dependency review
+   will want to know.
+3. **MSRV is enforced in practice:** building against the branch under
+   rustc 1.94 fails fast with a clear `requires rustc 1.96` error — good,
+   the pin does its job (not a seam regression; noted for reproducibility).
+
+## Reproducing
+
+```sh
+# clone cpex next to AI-Identity and fetch the PR head
+git clone https://github.com/contextforge-org/cpex ../../../cpex
+git -C ../../../cpex fetch origin pull/166/head:pr-166
+git -C ../../../cpex checkout pr-166
+
+# from this directory (rustup picks up cpex's 1.96 pin via override or default)
+cargo check --all-targets && cargo test
+```
+
+The committed `Cargo.lock` in this directory records the exact resolution
+used for this run.