ci(build): extend debuginfo=0 + mold to linux-build (fix recurring rust-lld SIGBUS)

.claude/board/AGENT_LOG.md

@@ -1,3 +1,9 @@
+## 2026-06-18 — CI: extend debuginfo=0 + mold to the `linux-build` job (link-cliff flake)
+
+**Main thread (Opus).** Branch `claude/ci-linux-build-debuginfo0-mold`. The `linux-build (stable)` job in `build.yml` flaked twice (#525, #528) with the `rust-lld` SIGBUS link cliff (signal 7, object truncated when the partition fills mid-link, crash in `llvm::parallelFor`). It was the ONLY job still linking the full lance+datafusion test set at workflow-level `debuginfo=1` and without mold — the `test` (TD-CI-TEST-JOB-DEBUGINFO0) and `test-with-coverage` (TD-CI-COVERAGE-MOLD-1) jobs in rust-test.yml already had both mitigations and are green.
+
+**Fix (additive, mirrors the green jobs exactly):** job-level `RUSTFLAGS: "-C debuginfo=0 -C target-cpu=x86-64-v3"` override (the load-bearing relief — ~73% smaller per-binary link footprint per the sibling-job measurements) + the pinned `rui314/setup-mold@9c9c13bf…` step before the Swatinem cache. 17 insertions, no deletions. YAML validated. Board: TD-CI-LINUX-BUILD-DEBUGINFO0 (Paid, confirm-on-green). No source/test change.
+
 ## 2026-06-18 — B2 resolved: witness-arc boundary documented (NO `WitnessArcEvaluator` trait)
 
 **Main thread (Opus) + 5+3 council**, branch `claude/witness-arc-boundary-doc`. The parked B2 item — "wire perturbation-sim witness arc into contract witness_table" — was put through the critical-decision protocol (5 analysts + 3 brutal critics, all read both files in full). **Unanimous verdict: do NOT build the trait.** The two "witness arc" notions are different objects (numeric `∑field·arc` standing wave vs W-slot→identity resolution); welding them is an AP6 one-impl trait + AGI-as-glove "never a new trait" violation + a CATCH-CRITICAL dep-direction inversion (zero-dep contract would gain a perturbation-sim dep). integration-lead confirmed the real wiring is downstream D-MBX-A3, gated on D-MBX-A2 (current gating gap) + OQ-11.2 + a §0 dep ruling.

.claude/board/TECH_DEBT.md

@@ -15,6 +15,21 @@
 
 ## Open Debt
 
+### TD-CI-LINUX-BUILD-DEBUGINFO0 — `linux-build` was the last job missing the link-cliff mitigation; debuginfo=0 + mold extended to it (2026-06-18)
+
+**Paid (this commit).** `build.yml`'s `linux-build (stable)` job linked the full
+lance+datafusion test-binary set at workflow-level `debuginfo=1` and **without
+mold** — the only job still missing the mitigation that `TD-CI-TEST-JOB-DEBUGINFO0`
+(the `test` job) and `TD-CI-COVERAGE-MOLD-1` (`test-with-coverage`) already carry.
+It flaked **twice** (#525, #528) with a hard `rust-lld` SIGBUS (signal 7, object
+file truncated when the link partition fills mid-link; crash in
+`llvm::parallelFor`). Fix mirrors the green sibling jobs exactly: job-level
+`RUSTFLAGS: "-C debuginfo=0 -C target-cpu=x86-64-v3"` (the load-bearing relief —
+shrinks per-binary link footprint ~73% so the partition can't fill) + the pinned
+`rui314/setup-mold` step. Additive only; first run after this change repopulates
+the job's Swatinem cache (job-level RUSTFLAGS = own cache key). **Confirm on the
+next few green `linux-build` runs that the SIGBUS does not recur.**
+
 ### TD-WITNESS-EVAL-WIRING-1 — perturbation-sim Parseval witness evaluator ↔ contract `WitnessTable` are shipped but unconnected by design (2026-06-18)
 
 **Open — intentionally deferred (5+3 council, B2).** `perturbation-sim::witness`

.github/workflows/build.yml

@@ -24,6 +24,18 @@ jobs:
   linux-build:
     runs-on: ubuntu-24.04
     timeout-minutes: 30
+    env:
+      # Override the workflow-level debuginfo=1 for this job (parity with the
+      # `test` + `test-with-coverage` jobs in rust-test.yml, TD-CI-TEST-JOB-DEBUGINFO0
+      # / TD-CI-COVERAGE-MOLD-1). This job links the SAME full lance+datafusion
+      # test-binary set at the SAME disk/RSS cliff and was the one job still
+      # missing the mitigation — it flaked twice with a hard `rust-lld` SIGBUS
+      # (signal 7 = object file truncated when the link partition fills mid-link,
+      # crashing in llvm::parallelFor). debuginfo carries no value in CI (no
+      # debugger is attached); dropping it cut per-binary link footprint ~73%
+      # in the sibling jobs. Note: a job-level RUSTFLAGS gives this job its own
+      # Swatinem cache key — the first run after this change repopulates it.
+      RUSTFLAGS: "-C debuginfo=0 -C target-cpu=x86-64-v3"
     defaults:
       run:
         working-directory: lance-graph
@@ -44,6 +56,11 @@ jobs:
         run: |
           rustup toolchain install ${{ matrix.toolchain }}
           rustup default ${{ matrix.toolchain }}
+      - name: Setup mold linker
+        # Parity with rust-test.yml: the heavy lance+datafusion build + test
+        # binaries hit the GNU-ld/rust-lld RSS+disk cliff at the link step
+        # (intermittent SIGBUS). mold links them fast + low-memory.
+        uses: rui314/setup-mold@9c9c13bf4c3f1adef0cc596abc155580bcb04444 # v1
       - uses: Swatinem/rust-cache@v2
         with:
           shared-key: "lance-graph-deps"