fix(features): gate 6 items on streamable-http/async + add lint-ci-no-default regression guard (Phase 8e, closes #295)

.github/workflows/pr-fast.yml

@@ -403,6 +403,38 @@ jobs:
           save-if: 'false'
       - run: cargo clippy --workspace --all-targets --all-features --locked --no-deps -- -D warnings
 
+  # ─────────────────────────────────────────────────────────────────────
+  # clippy-no-default — Phase 8e regression guard (issue #295).  Same
+  # strict clippy flag stack as `clippy` above but with
+  # `--no-default-features` instead of `--all-features`, catching items
+  # reachable only when a feature is enabled but not themselves
+  # `#[cfg(feature = "…")]`-gated.  Cache key is distinct from `clippy`
+  # because the feature configuration produces a different artifact set.
+  # ─────────────────────────────────────────────────────────────────────
+  clippy-no-default:
+    name: Clippy (--no-default-features)
+    runs-on: ubuntu-22.04
+    needs: [classify, sanity]
+    if: needs.classify.outputs.code == 'true'
+    timeout-minutes: 30
+    steps:
+      - uses: actions/checkout@de0fac2e4500dabe0009e67214ff5f5447ce83dd # v6.0.2
+        with:
+          ref: ${{ github.event.pull_request.head.sha || github.sha }}
+
+      - name: Free up disk space
+        run: |
+          sudo rm -rf /usr/local/lib/android /usr/share/dotnet /opt/ghc
+          sudo rm -rf /usr/local/share/boost /usr/local/graalvm
+          df -h /
+
+      - run: rustup show
+      - uses: Swatinem/rust-cache@c19371144df3bb44fab255c43d04cbc2ab54d1c4 # v2.9.1
+        with:
+          shared-key: pr-fast-clippy-no-default
+          save-if: 'false'
+      - run: cargo clippy --workspace --all-targets --no-default-features --locked --no-deps -- -D warnings
+
   # ─────────────────────────────────────────────────────────────────────
   # docs — rustdoc with `-Dwarnings` PLUS doctest execution.  Catches
   # the exact class of bug Phase 1 / Phase 2 locally catch too — keeping
@@ -661,6 +693,7 @@ jobs:
       - fmt
       - sanity
       - clippy
+      - clippy-no-default
       - docs
       - test-build
       - tests
@@ -687,6 +720,7 @@ jobs:
             [fmt]='${{ needs.fmt.result }}'
             [sanity]='${{ needs.sanity.result }}'
             [clippy]='${{ needs.clippy.result }}'
+            [clippy-no-default]='${{ needs.clippy-no-default.result }}'
             [docs]='${{ needs.docs.result }}'
             [test-build]='${{ needs.test-build.result }}'
             [tests]='${{ needs.tests.result }}'

crates/uffs-client/src/daemon_ctl.rs

@@ -183,6 +183,10 @@ pub(crate) fn verify_daemon_after_connect_strict_at(
 /// On Unix, opens the `AF_UNIX` socket at `sock_path`.
 /// On Windows, opens the named pipe (no `ws2_32` cost) — `sock_path` is
 /// unused but kept for API stability.
+///
+/// Only consumed by the async keepalive task, hence the `async` feature
+/// gate (matches `connect_keepalive` in `lib.rs`).
+#[cfg(feature = "async")]
 pub(crate) fn keepalive_send_blocking(sock_path: &std::path::Path) {
     #[cfg(unix)]
     {

crates/uffs-mcp/src/handler/mod.rs

@@ -321,9 +321,12 @@ impl ServerHandler for UffsMcpServer {
         .with_instructions(AGENT_INSTRUCTIONS.to_owned())
     }
 
-    #[expect(
-        clippy::cognitive_complexity,
-        reason = "async match + await + iteration + logging contributes to Clippy score"
+    #[cfg_attr(
+        feature = "streamable-http",
+        expect(
+            clippy::cognitive_complexity,
+            reason = "async match + await + iteration + logging contributes to Clippy score"
+        )
     )]
     async fn on_roots_list_changed(&self, context: rmcp::service::NotificationContext<RoleServer>) {
         // Ask the client for the current list of roots.
@@ -361,9 +364,12 @@ impl ServerHandler for UffsMcpServer {
         })
     }
 
-    #[expect(
-        clippy::cognitive_complexity,
-        reason = "tool dispatch with timing, error handling, stats, and reconnect"
+    #[cfg_attr(
+        feature = "streamable-http",
+        expect(
+            clippy::cognitive_complexity,
+            reason = "tool dispatch with timing, error handling, stats, and reconnect"
+        )
     )]
     async fn call_tool(
         &self,

crates/uffs-mcp/src/lib.rs

@@ -227,9 +227,12 @@ impl Default for McpConfig {
 ///
 /// Returns an error if the daemon connection fails or the MCP transport
 /// encounters an I/O error.
-#[expect(
-    clippy::cognitive_complexity,
-    reason = "MCP server startup with daemon connect, idle timer, and transport orchestration"
+#[cfg_attr(
+    feature = "streamable-http",
+    expect(
+        clippy::cognitive_complexity,
+        reason = "MCP server startup with daemon connect, idle timer, and transport orchestration"
+    )
 )]
 pub async fn run_mcp_server_with_config(config: &McpConfig) -> anyhow::Result<()> {
     info!(

crates/uffs-mcp/src/stats.rs

@@ -86,6 +86,10 @@ impl McpStats {
     }
 
     /// Average tool call latency in microseconds (0 if no calls).
+    ///
+    /// Only consumed by the HTTP `/status` endpoint, hence the
+    /// `streamable-http` feature gate.
+    #[cfg(feature = "streamable-http")]
     #[must_use]
     pub(crate) fn avg_tool_latency_us(&self) -> u64 {
         let total = self.total_tool_calls.load(Ordering::Relaxed);
@@ -96,6 +100,10 @@ impl McpStats {
     }
 
     /// Serialize stats to a JSON value for the `/status` endpoint.
+    ///
+    /// Only consumed by the HTTP `/status` endpoint, hence the
+    /// `streamable-http` feature gate.
+    #[cfg(feature = "streamable-http")]
     #[must_use]
     pub(crate) fn to_json(&self) -> serde_json::Value {
         serde_json::json!({

docs/architecture/code-quality/dependency_policy.md

@@ -52,7 +52,7 @@ test-substitution boundary documented in
 ## 2  The lint posture
 
 Phase 8 introduces **no new clippy lints**.  Feature and dependency
-hygiene is enforced through five complementary tools wired into the
+hygiene is enforced through six complementary tools wired into the
 pre-push gate and CI:
 
 | Tool | What it catches | Where |
@@ -62,6 +62,16 @@ pre-push gate and CI:
 | `cargo vet` | Unaudited crate-versions in the dep graph | `supply-chain/{config,audits,imports.lock}.toml` + `pr-fast.yml::security` |
 | `cargo tree --workspace -d` | Cross-version duplicate inventory | Surfaced by `scripts/dev/feature_dep_audit.sh --with-cargo`; no hard gate (workspace runs `multiple-versions = "warn"`) |
 | `cargo doc --no-deps --all-features` | Broken intra-doc links inside `# Features` sections | Pre-push gate (`rustdoc`) + `pr-fast.yml::docs` |
+| `cargo clippy --workspace --all-targets --no-default-features --no-deps -- -D warnings` | **Feature-additivity regressions** — `pub`/`pub(crate)` items reachable only when feature X is on but not themselves `#[cfg(feature = "X")]`-gated (manifests as `dead_code` warnings + unfulfilled `expect` warnings when feature X is off) | Pre-push gate (`lint-ci-no-default` — Phase 8e) + `pr-fast.yml::clippy-no-default` |
+
+The sixth tool — `lint-ci-no-default` — is the Phase 8e regression
+guard (issue #295).  It mirrors the existing `lint-ci` gate
+(`--all-features -D warnings`) but swaps in `--no-default-features`,
+so the pair establishes the **additivity invariant**: every item
+reachable only with feature X must compile cleanly both with feature X
+off AND with all features on.  Without this gate, the `--all-features`
+build masks the dead-code warning the `--no-default-features` build
+emits, and additivity regresses silently.
 
 `deny.toml` is configured at:
 
@@ -331,4 +341,5 @@ Append-only.  Each entry: date, sub-phase, decision, PR.
 |---|---|---|---|
 | 2026-05-19 | 8a | Add `scripts/dev/feature_dep_audit.sh` baseline tool | #292 |
 | 2026-05-19 | 8b | Document the 3 feature contracts per playbook §988 in rustdoc + Cargo.toml | #293 |
-| 2026-05-19 | 8c | Add this `dependency_policy.md` + `CONTRIBUTING.md` cross-link | this PR |
+| 2026-05-19 | 8c | Add this `dependency_policy.md` + `CONTRIBUTING.md` cross-link | #294 |
+| 2026-05-19 | 8e | Add `lint-ci-no-default` regression guard + fix 6 feature-additivity gaps (`McpStats::{avg_tool_latency_us,to_json}`, `keepalive_send_blocking`, 3 `cognitive_complexity` expects) | this PR |

docs/architecture/code-quality/trait_policy.md

@@ -190,5 +190,5 @@ Append-only.  Each entry: date, sub-phase, decision, PR.
 | 2026-05-19 | 7c | Audit 127 generic-fn sites — all G1/G2/G5; zero refactor PRs | findings-only |
 | 2026-05-19 | 7d | Audit 40 true dispatch sites — all D1/D2; zero refactor PRs | findings-only |
 | 2026-05-19 | 7e | Keep all 3 surviving `pub trait`s OPEN — `FileReader` (J3), `FormatRow` (J3), `RuntimeDir` (structurally sealed by private fields of `RuntimeFile`) | findings-only |
-| 2026-05-19 | 7f | Add 4 clippy lints: `too_many_arguments`, `trait_duplication_in_bounds`, `wrong_self_convention` (deny) + `multiple_bound_locations` (warn) | TBD |
+| 2026-05-19 | 7f | Add 4 clippy lints: `too_many_arguments`, `trait_duplication_in_bounds`, `wrong_self_convention` (deny) + `multiple_bound_locations` (warn) | #291 |
 | 2026-05-19 | 7g | Add this `trait_policy.md` + `CONTRIBUTING.md` cross-link | this PR |

just/test.just

@@ -69,6 +69,15 @@ lint-ci:
     @printf "\033[0;34m🚨 CI lint gating (FAST-FAIL)...\033[0m\n"
     cargo clippy --workspace --all-targets --all-features --no-deps -- -D warnings
 
+# Feature-additivity regression guard (Phase 8e — issue #295).  Runs the
+# same strict clippy flag stack as `lint-ci` but with `--no-default-features`
+# instead of `--all-features`, catching items that are reachable only when
+# a feature is enabled but not themselves `#[cfg(feature = "…")]`-gated.
+# MUST mirror .github/workflows/pr-fast.yml `clippy-no-default` job exactly.
+lint-ci-no-default:
+    @printf "\033[0;34m🚨 CI lint gating (--no-default-features, FAST-FAIL)...\033[0m\n"
+    cargo clippy --workspace --all-targets --no-default-features --no-deps -- -D warnings
+
 # Cross-platform CI lint gate via Docker (Linux target).
 # Catches Linux-only clippy drift that the local host (macOS) cannot reproduce
 # — e.g. platform-dependent type aliases like `libc::time_t` where nightly

scripts/ci/gates.toml

@@ -340,6 +340,46 @@ The exact clippy flag stack `pr-fast.yml`'s `clippy` job runs.
 Kept in lockstep manually until Phase 2 codegen lands.
 """
 
+[[gate]]
+id = "lint-ci-no-default"
+label = "CI-mirror clippy --no-default-features (-D warnings)"
+command = ["just", "lint-ci-no-default"]
+tiers = ["pre-push", "pr-fast"]
+gate_when = "rust_changed"
+hard = true
+tool = "cargo"
+expected_runtime_secs = 30
+bucket = "seq"
+order = 25
+consumer_names = { "pr-fast" = "clippy-no-default" }
+notes = """
+Phase 8e regression guard for issue #295 — feature additivity.
+
+`cargo clippy --workspace --no-default-features --all-targets -- -D warnings`
+catches the class of bug that surfaced post-Phase-8 closeout: items
+reachable only when feature X is on, but not themselves
+`#[cfg(feature = "X")]`-gated.  The existing `lint-ci` gate runs
+`--all-features` which masks the dead-code + unfulfilled-`expect`
+warnings these gaps emit.
+
+Specifically prevents regression of the 6 sites fixed by issue #295:
+- `uffs-mcp::McpStats::{avg_tool_latency_us,to_json}` (now
+  `cfg(feature = "streamable-http")`-gated).
+- `uffs-client::daemon_ctl::keepalive_send_blocking` (now
+  `cfg(feature = "async")`-gated).
+- 3 `cfg_attr(feature = "streamable-http", expect(cognitive_complexity, …))`
+  in `uffs-mcp::lib.rs` + `handler/mod.rs`.
+
+Mirrors `lint-ci` in flag stack and `-D warnings` strictness; differs
+only in `--no-default-features` instead of `--all-features`.  Together
+the two gates establish the additivity property: every `pub`/`pub(crate)`
+item reachable only with feature X must compile cleanly both with
+feature X off AND with all features on.
+
+Documented in
+`docs/architecture/code-quality/dependency_policy.md` §2.
+"""
+
 [[gate]]
 id = "rustdoc"
 label = "rustdoc -D warnings"

scripts/hooks/_lint_pre_push.sh

@@ -235,6 +235,7 @@ command -v reuse >/dev/null 2>&1 && spawn_bg "reuse" reuse lint --quiet
 if (( CODE_CHANGED )); then
     run_seq "cargo-check" cargo check --workspace --all-targets --all-features --locked
     run_seq "lint-ci" just lint-ci
+    run_seq "lint-ci-no-default" just lint-ci-no-default
     run_seq "lint-prod" just lint-prod
     run_seq "lint-tests" just lint-tests
     run_seq "rustdoc" env RUSTDOCFLAGS=-Dwarnings cargo doc --workspace --all-features --no-deps --locked