diff --git a/.github/workflows/release.yml b/.github/workflows/release.yml
index 5b7865e..db6ab80 100644
--- a/.github/workflows/release.yml
+++ b/.github/workflows/release.yml
@@ -5,11 +5,11 @@ on:
     tags:
       - 'v[0-9]*'
 
-# Least-privilege: this phase (T008) only validates the tag against the
-# workspace version and writes nothing. `contents: write` is deferred until
-# T012, the task that actually creates the GitHub Release -- granting it
-# here would hand a compromised validation step needless write access to
-# the repo via the default token.
+# Least-privilege: through T009 this workflow only reads the repo -- it
+# validates the tag, tests, and builds, but publishes nothing.
+# `contents: write` is deferred until T012, the task that actually creates
+# the GitHub Release -- granting it here would hand a compromised build
+# step needless write access to the repo via the default token.
 permissions:
   contents: read
 
@@ -33,3 +33,24 @@ jobs:
 
       - name: Validate release tag against workspace version (FR-002, FR-004, FR-010)
         run: .github/scripts/validate-release-tag.sh "${GITHUB_REF_NAME}"
+
+      - name: Install Rust toolchain
+        uses: dtolnay/rust-toolchain@e97e2d8cc328f1b50210efc529dca0028893a2d9 # v1
+        with:
+          toolchain: stable
+
+      - name: Cache cargo dependencies and build output
+        uses: Swatinem/rust-cache@c19371144df3bb44fab255c43d04cbc2ab54d1c4 # v2.9.1
+
+      - name: Test (cargo test --locked)
+        # --locked, not `make test`'s plain `cargo test`: an unlocked test
+        # run silently rewrites a drifted Cargo.lock, so by the time the
+        # --locked release build below runs, the lock would already be
+        # "fixed" and the drift it's meant to catch would never surface.
+        run: cargo test --locked
+
+      - name: Build release binary (FR-002)
+        # --locked: this is a release artifact users download -- fail loud
+        # if Cargo.lock has drifted from the manifests rather than silently
+        # building against dependency versions the lock file never recorded.
+        run: cargo build --release -p iklo-cli --locked
diff --git a/specs/005-ci-release-versioning/tasks.md b/specs/005-ci-release-versioning/tasks.md
index ce9ceb2..7bf24d2 100644
--- a/specs/005-ci-release-versioning/tasks.md
+++ b/specs/005-ci-release-versioning/tasks.md
@@ -181,9 +181,28 @@ created with the packaged CLI binary attached.
   packaging, checksums, and the atomic release-creation step are separate
   tasks (T009-T012) — this workflow does nothing on a real tag push yet
   beyond validating it.
-- [ ] **T009** [US2] Build the `iklo` executable in release mode
+- [x] **T009** [US2] Build the `iklo` executable in release mode
   (`cargo build --release -p iklo-cli`) only after `make test` passes
   (FR-002).
+  **Done 2026-08-13**: added toolchain install + `Swatinem/rust-cache`
+  (same pinned SHAs as `ci.yml`, confirmed byte-identical) to
+  `release.yml`, then `make test`, then `cargo build --release -p
+  iklo-cli --locked` as the final step. `--locked` added after
+  self-review: a release artifact should fail loud on `Cargo.lock` drift
+  rather than silently building against unrecorded dependency versions.
+  No `make build` (debug) step — T009's scope is only the release build,
+  gated on tests passing, not a redundant debug build first. Verified
+  locally: `make test` exits 0, `cargo build --release -p iklo-cli
+  --locked` exits 0 and produces `target/release/iklo`. Also updated the
+  workflow's least-privilege header comment, which still described the
+  T008-only state before this task added test/build steps.
+  Follow-up fix
+  after cubic-dev-ai review: the test step now runs `cargo test --locked`
+  directly rather than `make test`'s plain `cargo test` -- an unlocked
+  test run silently rewrites a drifted `Cargo.lock`, which would have
+  defeated the release build's own `--locked` guarantee by the time it
+  ran. Scoped to `release.yml` only, not `Makefile`/`ci.yml` (those are a
+  separate concern about local-dev/PR-check strictness, not this task).
 - [ ] **T010** [US2] Package and upload the built executable as a GitHub
   Release asset (FR-003, SC-002).
 - [ ] **T011** [US2] Generate and publish SHA-256 checksums for every