diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index 48d2b409009..90ec2be0398 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: ""
@@ -108,7 +107,6 @@ 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 +143,6 @@ 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
@@ -332,7 +329,6 @@ 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..3dbb77236ee 100644
--- a/ROADMAP.md
+++ b/ROADMAP.md
@@ -429,7 +429,7 @@ Tracked debt not dispatched with the 2026-04-21 lane wave (Lane 1e P3.0, SG-2c-4
   - **Lane E-I — port `SubValueRelation` + inductive fields + cost algebra (M)**: port Tier 1 (structural) + Tier 2 (lattice) + Tier 3 (`CostBound` + master theorem). Requires E-T, E-C. Pre-flight: verify v3 lowers `CostBound`'s self-referential-through-`List` shape. Acceptance: carrier types ported with round-trip tests; no lens row moves on E-I alone because consumer-visible facts still wait for E-P producer/consumer wiring.
   - **Lane E-P — per-call descent-evidence provenance (M)**: first P-c side-table producer slice has landed as `v3_compiler::dag::per_call_descent_evidence` (recursive self-call / arithmetic descent; unproven edges fail closed; `TransformNode` stays unwidened). v2 stores this class of fact on `ExprCall.descent_evidence` (`src/v2/00_core.dag:199`); v3 derives it off-substrate for now. Requires E-T, E-C, E-I. Remaining acceptance: cost/complexity lenses consume the side table, plus a v2-oracle-vs-v3 cementing test against `expr_call_descent_evidence`; carrier parity for `cost.dag` / `complexity.dag` on the non-method-dispatch slice closes there.
   - **Lane E-M — `MethodSemantics` port-or-subsume (S–M)**: **closed via M-b structural subsumption.** Transitive facts (`CollectionSizeEffect` / `CostShape` / `AlgebraFieldTemplate`) remain algebra-declaration facts; v3 method-like calls dispatch through `TransformTarget::{Callable, FieldProject, Operator}` and typed declaration/effect metadata. No `src/v3/std/method_semantics.dag`, no Rust mirror, and no `ExprMethodCall` attachment point.
-- **CI ratchet architecture — PARTIAL (T-Receipts W1 second bundle)**: surfaced during the 2026-04-21 reflective analysis (`53b3110..ae8825a` range). Commits `37cd6128`, `4898983e`, `f84ed355` hardened the ratchet against CI-log instability, but `2d8396df` widened the exemption list. `scripts/slow-test-exemptions.txt` currently has **39** active non-comment exemptions; `scripts/check-test-timeout.sh` meta-ratchet default `TEST_TIMEOUT_MAX_EXEMPTIONS` matches that count. **Landed partial:** classification audit [docs/debt/ci-ratchet-exemption-audit-2026-04-24.md](docs/debt/ci-ratchet-exemption-audit-2026-04-24.md) (2026-04-24 baseline) plus follow-up routing audit [docs/debt/ci-ratchet-exemption-audit-2026-05-02.md](docs/debt/ci-ratchet-exemption-audit-2026-05-02.md) (bounded scope — not a completed Phase 1 per-test timing pass). **Still open:** fresh CI-shaped per-test timing audit, stale exemption deletion if any entries measure under 2s, and per-exempt duration budgets once fresh timings exist. Dispatch brief: `docs/briefs/ci-ratchet-architecture-audit.md`.
+- **CI ratchet architecture — PARTIAL (T-Receipts W1 second bundle)**: surfaced during the 2026-04-21 reflective analysis (`53b3110..ae8825a` range). Commits `37cd6128`, `4898983e`, `f84ed355` hardened the ratchet against CI-log instability, but `2d8396df` widened the exemption list. `scripts/slow-test-exemptions.txt` currently has **40** active non-comment exemptions; `scripts/check-test-timeout.sh` meta-ratchet default `TEST_TIMEOUT_MAX_EXEMPTIONS` matches that count (floor **39→40** on 2026-05-05: T-Demo runner-visibility exemption on gunbc#1798). **Landed partial:** classification audit [docs/debt/ci-ratchet-exemption-audit-2026-04-24.md](docs/debt/ci-ratchet-exemption-audit-2026-04-24.md) (2026-04-24 baseline) plus follow-up routing audit [docs/debt/ci-ratchet-exemption-audit-2026-05-02.md](docs/debt/ci-ratchet-exemption-audit-2026-05-02.md) (bounded scope — not a completed Phase 1 per-test timing pass). **Still open:** fresh CI-shaped per-test timing audit, stale exemption deletion if any entries measure under 2s, and per-exempt duration budgets once fresh timings exist. Dispatch brief: `docs/briefs/ci-ratchet-architecture-audit.md`.
 - **`IntegrationRsScan` / `integration_rs_active_line_contains` in `src/v3/compiler/tests/integration/common/mod.rs` is a latent source of byte-constant workarounds in downstream tests** (T-Receipts, surfaced by T-Demo #686). The scanner is "deliberately narrow" and does not model Rust character literals, so any test author touching a file in its scan path cannot write `b'\\'` / `b'"'` directly and must substitute numeric byte constants (e.g., `92` / `34`) instead. Historical evidence: #686's text-slicing helper introduced `DAG_ESCAPE_BYTE` / `DAG_QUOTE_BYTE` constants for exactly this reason; #705 deleted the helper when `TestRunner::run_suite` obsoleted it, and the constants went with it — so there is **no surviving in-tree instance of the workaround today**. The scanner constraint itself remains, which means the next test author landing in the scan path will recreate the pattern. Dissolution: either widen the scanner to model Rust char literals, or replace its scan with a structural reader that doesn't need to exclude char-literal syntax. Small scope; cosmetic for now, but the constraint is a workaround attractor. Owner: unassigned; P2 Boundary Discipline / T-Receipts bundle.
 - **Stale-receipt sweep in `docs/briefs/` — PARTIAL (T-Receipts W1).** The cited `DeclarationLookup` cleanup brief now carries a historical-receipt banner stating the lane is closed by SG-4b-1-fix and that `DeclarationLookup` / `find_declaration` are gone from `src/v3/lenses/variant_payload.dag`; its stale INVARIANTS refs were also updated to stable anchors. Remaining broad `docs/briefs/` sweep stays open for later post-wave stale claims. **Include:** `docs/design-pure-bootstrap.md`'s hand-maintained count ("78 hand-maintained .rs files") was stale vs. the SG-0 census — **CLOSED in this R1 PR**: all five occurrences (lines 7, 49, 82, 105, 242 of the design doc) now point at the live census, reframed as deltas against the illustrative 78-file baseline, or scoped to the non-test + TESTING residual framing. No frozen absolute count remains.
 - **Compiler–`std/` consolidation program — specific migrations**: end-state defined in [docs/thesis/compiler-std-consolidation.md](docs/thesis/compiler-std-consolidation.md). Each of the migrations below is a standalone lane; together they collapse the compiler-specific type surface toward the positive definition (pipeline + regen + lens-specific return-type carriers + accessor). **Ratchet:** count of `type` declarations in `src/v3/compiler/*.dag` AND `src/v3/lenses/*.dag` that are NOT in the positive-def set AND NOT exempted → 0. Positive-def: pipeline/regen types + lens-API return carriers (`Origin`, `UnusedParameter`, `VariantPayloadShapeLookup` 3-variant, `TemplateArgumentBinding` semantic carrier, etc.). Exempted: `parse_tables.dag` (7 types, pending SG-2c-proper per-row classification). In-ratchet: **workaround-shaped infer-helper coproducts with named dissolution triggers (`TemplateArgumentsMatch`, `TemplateArgumentCursor`, `NormalizedInstantiationArgs`)** — Lookup-pattern carriers on lens surfaces import `v3.std.lookup::Lookup` (`complexity`, `cost`, `infer_helpers`). Primary count: 3. See thesis doc table for per-file disposition.
@@ -623,6 +623,10 @@ Five novel-finding rows surfaced by the 2026-05-04 Exploratory + Reflective inge
 
 R3 Debt-Paydown ledger receipts and routing detail at [docs/debt/r3-debt-paydown-ledger-2026-05-02.md](docs/debt/r3-debt-paydown-ledger-2026-05-02.md).
 
+### Post-merge debt (2026-05-05 R3 substrate — rust-toolchain channel authority)
+
+- **`rust_toolchain_toml_codegen_from_rustup_dag`** *(literal duplicate **retired** 2026-05-05, #1798 / api-review)*: `dsl/extdeps/rustup.dag` previously carried `data ci_pinned_toolchain` parallel to `rust-toolchain.toml` — P2 dual-authority. **Resolution:** removed `ci_pinned_toolchain`; repo-root `rust-toolchain.toml` is the **sole** hand-maintained channel + components pin; `extdeps/rustup.dag` documents rustup’s role and points at that file only (no second string). **Optional follow-on** if `gunbc/ci.dag` / workflow-as-data later needs a typed `.dag` carrier for the pin: generate or parse-assert from `rust-toolchain.toml`, never a second hand-authored literal. Surfaced R3 Substrate Mgr + scheduled api-review on toolchain PR quartet ([PR #1789 review comment](https://github.com/gunb-ai/gunbc/pull/1789#issuecomment-4381694920)).
+
 ## What NOT to build yet
 
 - Any fourth per-language emit file before Stage 1e consolidation finishes.
diff --git a/dsl/extdeps/github/actions.dag b/dsl/extdeps/github/actions.dag
index 40878c6efba..e3bfbad77fc 100644
--- a/dsl/extdeps/github/actions.dag
+++ b/dsl/extdeps/github/actions.dag
@@ -202,7 +202,9 @@ 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..159fe9c91bf 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 channel in repo-root rust-toolchain.toml (read by CI
+//     `actions-rust-lang/setup-rust-toolchain` after checkout)
 //
 // 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 extdeps/github/actions.dag
+// `setup_rust_action`). Local dev follows rust-toolchain.toml via rustup.
 //
 // Future:
 //   When we model toolchain switching, channels, components, or
@@ -44,9 +45,14 @@ data rustup_install_url: NonEmptyStr = "https://rustup.rs"
 // Default channel we expect when "rustup default" is queried.
 data default_channel: RustChannel = Stable
 
-// The pinned toolchain version used in CI. Local dev usually tracks
-// stable; CI pins for reproducibility.
-data ci_pinned_toolchain: NonEmptyStr = "1.93.0"
+// Pinned **channel** string for this repo lives only in repo-root
+// `rust-toolchain.toml` `[toolchain].channel` (CI `setup-rust-toolchain` and
+// local rustup read that file after checkout). `[toolchain].components` is
+// also declared there, but `.github/workflows/ci.yml` may still pass
+// per-job `components:` inputs; the action unions them — not a second channel
+// authority. Do not add a second channel literal here; collapsing components
+// to a single workflow projection is workflow-as-data / ROADMAP
+// `rust_toolchain_toml_codegen_from_rustup_dag` follow-on.
 
 // Rustup docs URL for reference.
 data rustup_docs: NonEmptyStr = "https://rust-lang.github.io/rustup/"
diff --git a/rust-toolchain.toml b/rust-toolchain.toml
index 7828a71dec7..96bb73ab226 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 and components for local rustup and GitHub Actions.
+# `actions-rust-lang/setup-rust-toolchain` reads this file after checkout.
+# Sole hand-maintained toolchain pin for this repo (see `dsl/extdeps/rustup.dag`).
 [toolchain]
 channel = "1.93.0"
 components = ["clippy", "rustfmt"]
diff --git a/scripts/check-test-timeout.sh b/scripts/check-test-timeout.sh
index 928c4976c82..48667af3ad3 100755
--- a/scripts/check-test-timeout.sh
+++ b/scripts/check-test-timeout.sh
@@ -46,7 +46,7 @@
 #                         (default scripts/slow-test-exemptions.txt).
 #   TEST_TIMEOUT_MAX_EXEMPTIONS
 #                         Ratchet floor for active exemption entries
-#                         (default 39, captured 2026-04-25). Lower this
+#                         (default 40, captured 2026-05-05). Lower this
 #                         value in the same PR that removes exemptions.
 
 set -euo pipefail
@@ -55,7 +55,7 @@ log_file_arg=${1:-}
 budget_ms=${2:-${TEST_TIMEOUT_MS:-2000}}
 pkg=${TEST_TIMEOUT_PACKAGE:-v3-compiler}
 exempt_file=${TEST_TIMEOUT_EXEMPT:-scripts/slow-test-exemptions.txt}
-max_exemptions=${TEST_TIMEOUT_MAX_EXEMPTIONS:-39}
+max_exemptions=${TEST_TIMEOUT_MAX_EXEMPTIONS:-40}
 
 script_dir=$(cd "$(dirname "$0")" && pwd)
 repo_root=$(cd "$script_dir/.." && pwd)
diff --git a/scripts/slow-test-exemptions.txt b/scripts/slow-test-exemptions.txt
index 8bf6d06e206..ce8b3857a42 100644
--- a/scripts/slow-test-exemptions.txt
+++ b/scripts/slow-test-exemptions.txt
@@ -77,4 +77,6 @@ sg2_parse_authority_test::parse_surface_dag_compiles_cleanly_for_regen_parse  #
 sg2c1_parse_tables_authority_test::parse_tables_generated_module_matches_checked_in_snapshot  # SG-2c-1 grammar-tables prototype snapshot: in-process authority compile (parse_tables.dag + tokenize.dag) + rustfmt stdout; same paydown class as SG-1 tokenize / SG-2 parse snapshot gates.
 sg6_hand_authored_census_test::sg6_regen_lens_cli_smoke_regenerates_named_entry_without_drift  # SG-6 regen CLI smoke intentionally shells out to regen path; CLI smoke cost is tracked in SG-6, not TM-0.
 
+t_demo_fixture_test::t_demo_canonical_suites_are_runner_visible  # ROADMAP R1 §T-Demo: `compile_to_dag` on `t_demo_fixtures.dag` + `TestRunner` over two canonical suites; cold GHA can exceed 2s wall (2565ms observed). Paydown: shared fixture compile / runner setup with adjacent T-Demo integration tests (TESTING.md §shared-setup), not TM-0.
+
 thesis_validation_test::kf_1_structural_list_operation_ordering_holds  # KF-1 thesis validation remains compile-heavy on CI runners; TESTING.md test-shape paydown owns future decomposition, not TM-0.