diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index 48d2b409009..9272e95dc94 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -49,7 +49,6 @@ jobs:
       - name: Setup Rust
         uses: actions-rust-lang/setup-rust-toolchain@v1.16.0
         with:
-          toolchain: "1.93.0"
           components: rustfmt
           cache: false
           rustflags: ""
@@ -77,6 +76,9 @@ jobs:
         with:
           fetch-depth: 1
 
+      - name: Rust toolchain pin alignment (rust-toolchain.toml vs rustup.dag)
+        run: bash scripts/check-rust-toolchain-pin-alignment.sh
+
       - name: Fabrication sentinel ratchet (P0-C)
         run: bash scripts/check-fabrication-sentinels.sh
 
@@ -108,7 +110,6 @@ jobs:
       - name: Setup Rust
         uses: actions-rust-lang/setup-rust-toolchain@v1.16.0
         with:
-          toolchain: "1.93.0"
           components: rustfmt
           cache: false
           rustflags: ""
@@ -145,7 +146,6 @@ jobs:
       - name: Setup Rust
         uses: actions-rust-lang/setup-rust-toolchain@v1.16.0
         with:
-          toolchain: "1.93.0"
           # Integration snapshot tests (`regen_parse` path, lane2d cost lens, …) shell out to `rustfmt`.
           components: rustfmt, clippy
           cache: false
@@ -192,14 +192,14 @@ jobs:
       # miss, first compile + link on ubuntu-latest) can spend minutes — keep
       # headroom beyond a tight 120s; per-test discipline lives in
       # `tests/common/budgeted.rs` (DEFAULT_BUDGET_MS).
-      - name: v3 tests (Stage 2d integration module, 300s cold-compile-safe budget)
+      - name: v3 tests (Stage 2d integration module, 420s cold-compile-safe budget)
         run: |
           start=$(date +%s)
           cargo test -p v3-compiler --test integration lane2_stage_2d_symbolic_cost_test::
           elapsed=$(( $(date +%s) - start ))
           echo "v3 Stage 2d (lane2d) wall time: ${elapsed}s"
-          if [ "$elapsed" -gt 300 ]; then
-            echo "::error::v3 lane2d tests took ${elapsed}s (budget: 300s) — share bootstrap setup via OnceLock or collapse fine-grained tests"
+          if [ "$elapsed" -gt 420 ]; then
+            echo "::error::v3 lane2d tests took ${elapsed}s (budget: 420s) — share bootstrap setup via OnceLock or collapse fine-grained tests"
             exit 1
           fi
 
@@ -213,12 +213,14 @@ jobs:
       # `RUSTC_BOOTSTRAP=1` prefix is the documented narrow unlock for libtest flags
       # and does not enable unstable language features.
       - name: v3 tests (full suite, 2400s transitional budget)
+        id: v3_full_suite
         env:
           # Keep libtest lines plain for `scripts/check-test-timeout.sh` (Phase-0
           # ratchet); workflow-level `CARGO_TERM_COLOR=always` would otherwise
           # inject ANSI into cargo's stream.
           CARGO_TERM_COLOR: never
         run: |
+          rm -f /tmp/v3-test-timings.log
           start=$(date +%s)
           RUSTC_BOOTSTRAP=1 cargo test -p v3-compiler -- -Z unstable-options --report-time 2>&1 | tee /tmp/v3-test-timings.log
           status=${PIPESTATUS[0]}
@@ -241,12 +243,12 @@ jobs:
       # `src/v3/compiler/tests/HANDOFF_PHASE0.md` (TESTING.md § test layers,
       # `feedback_test_timeout_2s`).
       #
-      # **`if: always()`** — the ratchet report is still useful on red runs
-      # (full-suite failure, 2400s transitional-budget overflow). The log is captured via
-      # `tee` before the enforcement check, so partial timing data survives
-      # failure and the ratchet can still emit actionable slow-test output.
+      # Run only when the full-suite step actually executed (success or failure).
+      # If an earlier step (e.g. lane2d budget) aborts the job, `v3_full_suite` is
+      # skipped — do not parse a stale `/tmp/v3-test-timings.log` from a prior
+      # step or runner reuse (`if: always()` alone is insufficient).
       - name: v3 tests (per-test 2s ratchet)
-        if: always()
+        if: always() && (steps.v3_full_suite.outcome == 'success' || steps.v3_full_suite.outcome == 'failure')
         run: |
           if [ ! -s /tmp/v3-test-timings.log ]; then
             echo "::notice::no timing log captured or log is empty (full-suite step did not reach cargo test, or tee wrote nothing) — skipping per-test ratchet"
@@ -332,7 +334,6 @@ jobs:
       - name: Setup Rust
         uses: actions-rust-lang/setup-rust-toolchain@v1.16.0
         with:
-          toolchain: "1.93.0"
           cache: false
           rustflags: ""
 
diff --git a/ROADMAP.md b/ROADMAP.md
index 7be8f9cbf4e..26e4a8e572f 100644
--- a/ROADMAP.md
+++ b/ROADMAP.md
@@ -385,6 +385,7 @@ Per-row tagging is a scheduled follow-up sweep — **trigger:** post-merge of th
 - **`effects.dag` dual authority** — `dsl/std/effects.dag` (395 lines) vs `src/v3/std/effects.dag` (818 lines, diverged 2×). Dissolution: decide authoritative location, collapse the other; name a convergence lane.
 - **`container_template_algebra_rows` table duplicates type aliases** — `dsl/std/types.dag:133-146` is the string-keyed table (renamed from `container_to_algebra` in PR #651's narrow dissolution); `types.dag:211-213` declares `type List<T> = FreeMonoid<T>` etc. Dissolution: derive the table from the aliases when alias reflection lands.
 - **Parallel string-keyed authorities in types.dag + coercion.dag**: `kernel_primitives` (65-74), `container_arity` (79-91), `ordered_collections` (125-130), `TypeCheckpoint.dag_name: String` (38-44), `InhabitantDecl.algebra: String` (59-65). Header labels as transitional. Dissolution: derive from structural declarations.
+- **`rust-toolchain.toml` vs `dsl/extdeps/rustup.dag::ci_pinned_toolchain`**: the pinned rustc channel string lives in both the repo-root TOML (rustup + `setup-rust-toolchain` after checkout) and `data ci_pinned_toolchain` in the extdep stub — P2 parallel-authority drift risk. PR #1789 removed a false “codegen” banner and documented alignment; it did not introduce the duplication (the TOML was already hand-maintained). Dissolution trigger: **`rust_toolchain_toml_codegen_from_rustup_dag`** — regenerate `rust-toolchain.toml` from `rustup.dag` (or fold `ci_pinned_toolchain` into a single file-backed authority) via bounded `gunbc-codegen` (or successor) so only one authored pin remains. Owner: T-Workflow-As-Data / extdeps hygiene as bandwidth allows.
 
 ### P3 — modeling gaps
 
diff --git a/dsl/extdeps/github/actions.dag b/dsl/extdeps/github/actions.dag
index 40878c6efba..8518f687cef 100644
--- a/dsl/extdeps/github/actions.dag
+++ b/dsl/extdeps/github/actions.dag
@@ -202,7 +202,7 @@ data checkout_action: ActionRef = ActionRef {
 }
 
 data setup_rust_action: ActionRef = ActionRef {
-  owner: "dtolnay", repo: "rust-toolchain", ref: "stable"
+  owner: "actions-rust-lang", repo: "setup-rust-toolchain", ref: "v1.16.0"
 }
 
 data cache_action: ActionRef = ActionRef {
diff --git a/dsl/extdeps/rustup.dag b/dsl/extdeps/rustup.dag
index f1a5b6bd77f..f5b0e506944 100644
--- a/dsl/extdeps/rustup.dag
+++ b/dsl/extdeps/rustup.dag
@@ -11,15 +11,16 @@
 // What we actually depend on from rustup:
 //   - cargo binary, installed by default with the stable toolchain
 //   - rustc, installed by default
-//   - Pinned toolchain "1.93.0" in CI (.github/workflows/ci.yml)
+//   - Pinned toolchain "1.93.0" in repo-root rust-toolchain.toml (CI reads it)
 //
 // What we do NOT currently depend on:
 //   - Custom components (clippy ships with stable, rustfmt ships with stable)
 //   - Cross-compilation targets (gunbc only builds for the host)
 //   - Multiple toolchains (no toolchain switching)
 //
-// The CI workflow uses dtolnay/rust-toolchain@v1 to provision
-// rustup. Local dev uses whatever rustup ships as stable.
+// CI uses actions-rust-lang/setup-rust-toolchain (see setup_rust_action in
+// extdeps/github/actions.dag); channel comes from rust-toolchain.toml. Local dev
+// usually tracks stable unless overridden by that file.
 //
 // Future:
 //   When we model toolchain switching, channels, components, or
diff --git a/rust-toolchain.toml b/rust-toolchain.toml
index 7828a71dec7..15d812021a8 100644
--- a/rust-toolchain.toml
+++ b/rust-toolchain.toml
@@ -1,5 +1,6 @@
-# Generated by gunbc-codegen. Do not edit manually.
-# Source of truth: dsl/config/toolchain.dag
+# Channel pin for local rustup and GitHub Actions (`setup-rust-toolchain` reads
+# this file after checkout when no explicit `toolchain:` input is passed).
+# Keep `channel` aligned with `dsl/extdeps/rustup.dag` `ci_pinned_toolchain`.
 [toolchain]
 channel = "1.93.0"
 components = ["clippy", "rustfmt"]
diff --git a/scripts/check-rust-toolchain-pin-alignment.sh b/scripts/check-rust-toolchain-pin-alignment.sh
new file mode 100755
index 00000000000..2216e831bc0
--- /dev/null
+++ b/scripts/check-rust-toolchain-pin-alignment.sh
@@ -0,0 +1,30 @@
+#!/usr/bin/env bash
+# Fail closed if rust-toolchain.toml [toolchain].channel drifts from
+# dsl/extdeps/rustup.dag `ci_pinned_toolchain` while both remain hand-authored
+# (ROADMAP P2 / rust_toolchain_toml_codegen_from_rustup_dag).
+set -euo pipefail
+repo_root=$(cd "$(dirname "$0")/.." && pwd)
+cd "$repo_root"
+
+toml_channel=$(
+  grep -E '^[[:space:]]*channel[[:space:]]*=' rust-toolchain.toml |
+    head -1 |
+    sed -E 's/^[[:space:]]*channel[[:space:]]*=[[:space:]]*"([^"]+)".*/\1/'
+)
+dag_channel=$(
+  grep -E '^data ci_pinned_toolchain' dsl/extdeps/rustup.dag |
+    head -1 |
+    sed -E 's/^data ci_pinned_toolchain:[^=]*=[[:space:]]*"([^"]+)".*/\1/'
+)
+
+if [ -z "${toml_channel}" ] || [ -z "${dag_channel}" ]; then
+  echo "::error::could not parse channel from rust-toolchain.toml and/or ci_pinned_toolchain from dsl/extdeps/rustup.dag"
+  exit 1
+fi
+
+if [ "${toml_channel}" != "${dag_channel}" ]; then
+  echo "::error::Rust toolchain pin mismatch: rust-toolchain.toml channel='${toml_channel}' vs dsl/extdeps/rustup.dag ci_pinned_toolchain='${dag_channel}'. Align both until rust_toolchain_toml_codegen_from_rustup_dag dissolves the duplicate (ROADMAP.md P2)."
+  exit 1
+fi
+
+echo "Rust toolchain pin alignment OK (${toml_channel})."
diff --git a/src/v3/compiler/tests/integration.rs b/src/v3/compiler/tests/integration.rs
index 14301b9a78d..0ad20b1ea43 100644
--- a/src/v3/compiler/tests/integration.rs
+++ b/src/v3/compiler/tests/integration.rs
@@ -205,6 +205,7 @@ mod t_demo_fixture_test {
 
     use std::fs;
     use std::path::PathBuf;
+    use std::sync::OnceLock;
 
     use v3_compiler::compile_to_dag;
     use v3_compiler::dag::Dag;
@@ -216,6 +217,9 @@ mod t_demo_fixture_test {
     /// Byte-sync with `t_demo_structural_cost_obligation_gate.source` in `t_demo_fixtures.dag`.
     const T_DEMO_STRUCTURAL_COST_OBLIGATION_CLAIM_SOURCE: &str = "fn pair_score(xs: List<Int>) -> Int = fold(xs, 0, |outer, x| outer + fold(xs, 0, |inner, y| inner + x + y))\nlet complexity_demo_out: Int = pair_score(cons(1, singleton(2)))\n";
 
+    // Process-wide cache: shared read-only `Dag`; tests that mutate or need isolation must compile locally.
+    static T_DEMO_FIXTURE_DAG: OnceLock<Dag> = OnceLock::new();
+
     fn fixture_source() -> String {
         let path = PathBuf::from(env!("CARGO_MANIFEST_DIR"))
             .join("../../..")
@@ -227,11 +231,16 @@ mod t_demo_fixture_test {
         compile_to_dag(source, FIXTURE).expect("T-Demo fixture skeleton compiles")
     }
 
+    fn shared_t_demo_fixture_dag() -> &'static Dag {
+        T_DEMO_FIXTURE_DAG.get_or_init(|| {
+            let source = fixture_source();
+            compile_fixture(&source)
+        })
+    }
+
     #[test]
     fn t_demo_fixture_skeleton_compiles() {
-        let source = fixture_source();
-        let dag = compile_fixture(&source);
-
+        let dag = shared_t_demo_fixture_dag();
         assert!(
             dag.diagnostics().is_empty(),
             "T-Demo fixture skeleton should compile without diagnostics: {:?}",
@@ -239,27 +248,30 @@ mod t_demo_fixture_test {
         );
     }
 
+    fn assert_t_demo_canonical_suite_passes(dag: &Dag, suite_name: &str) {
+        let results = TestRunner::new(dag).run_suite(suite_name);
+        assert!(
+            !results.is_empty(),
+            "T-Demo suite `{suite_name}` should contain Day-1 Compiles claims"
+        );
+        assert!(
+            results
+                .iter()
+                .all(|result| result.result == ClaimResult::Pass),
+            "T-Demo suite `{suite_name}` should pass Day-1 Compiles claims, got {results:?}"
+        );
+    }
+
     #[test]
-    fn t_demo_canonical_suites_are_runner_visible() {
-        let source = fixture_source();
-        let dag = compile_fixture(&source);
+    fn t_demo_fixture_compiler_nerd_canonical_suite_is_runner_visible() {
+        let dag = shared_t_demo_fixture_dag();
+        assert_t_demo_canonical_suite_passes(dag, "fixture_compiler_nerd_canonical");
+    }
 
-        for suite_name in [
-            "fixture_compiler_nerd_canonical",
-            "fixture_integration_canonical",
-        ] {
-            let results = TestRunner::new(&dag).run_suite(suite_name);
-            assert!(
-                !results.is_empty(),
-                "T-Demo suite `{suite_name}` should contain Day-1 Compiles claims"
-            );
-            assert!(
-                results
-                    .iter()
-                    .all(|result| result.result == ClaimResult::Pass),
-                "T-Demo suite `{suite_name}` should pass Day-1 Compiles claims, got {results:?}"
-            );
-        }
+    #[test]
+    fn t_demo_fixture_integration_canonical_suite_is_runner_visible() {
+        let dag = shared_t_demo_fixture_dag();
+        assert_t_demo_canonical_suite_passes(dag, "fixture_integration_canonical");
     }
 
     /// ROADMAP T-Demo / PR #764: `FailsWithDiagnostic.detail_contains` must pin the **sum
@@ -283,9 +295,8 @@ mod t_demo_fixture_test {
 
     #[test]
     fn t_demo_impossible_bug_suite_r1_passes() {
-        let source = fixture_source();
-        let dag = compile_fixture(&source);
-        let results = TestRunner::new(&dag).run_suite("impossible_bug_class_suite_r1");
+        let dag = shared_t_demo_fixture_dag();
+        let results = TestRunner::new(dag).run_suite("impossible_bug_class_suite_r1");
         assert_eq!(results.len(), 2);
         assert!(
             results
@@ -301,9 +312,8 @@ mod t_demo_fixture_test {
     /// surface is user-extensible (THESIS §"User-defined dimensions").
     #[test]
     fn t_demo_user_authored_lens_rejects_violating_program_passes() {
-        let source = fixture_source();
-        let dag = compile_fixture(&source);
-        let results = TestRunner::new(&dag)
+        let dag = shared_t_demo_fixture_dag();
+        let results = TestRunner::new(dag)
             .run_suite("demo_user_authored_lens_rejects_violating_program_suite");
         assert_eq!(results.len(), 1);
         assert!(