ci: report sccache stats from the build server

.github/workflows/android-build.yml

@@ -65,7 +65,7 @@ jobs:
 
       - name: Show sccache stats
         if: always()
-        run: nix develop --no-update-lock-file .#android -c sccache --show-stats
+        run: nix develop --no-update-lock-file .#android -c ./scripts/ci/sccache-stats.sh
 
       - name: Collect Android release checksums
         run: |

.github/workflows/android-pr-build.yml

@@ -59,7 +59,7 @@ jobs:
 
       - name: Show sccache stats
         if: always()
-        run: nix develop --no-update-lock-file .#android -c sccache --show-stats
+        run: nix develop --no-update-lock-file .#android -c ./scripts/ci/sccache-stats.sh
 
       - name: Upload Android fake signed PR artifacts
         uses: actions/upload-artifact@ea165f8d65b6e75b540449e92b4886f43607fa02 # was v4

.github/workflows/desktop-build.yml

@@ -55,7 +55,7 @@ jobs:
 
       - name: Show sccache stats
         if: always()
-        run: nix develop --no-update-lock-file .#ci -c sccache --show-stats
+        run: nix develop --no-update-lock-file .#ci -c ./scripts/ci/sccache-stats.sh
 
       - name: Collect macOS release checksums
         run: |
@@ -133,7 +133,7 @@ jobs:
 
       - name: Show sccache stats
         if: always()
-        run: nix develop --no-update-lock-file .#desktop-linux -c sccache --show-stats
+        run: nix develop --no-update-lock-file .#desktop-linux -c ./scripts/ci/sccache-stats.sh
 
       - name: Collect Linux release checksums
         run: |

.github/workflows/desktop-pr-build.yml

@@ -42,7 +42,7 @@ jobs:
 
       - name: Show sccache stats
         if: always()
-        run: nix develop --no-update-lock-file .#ci -c sccache --show-stats
+        run: nix develop --no-update-lock-file .#ci -c ./scripts/ci/sccache-stats.sh
 
       - name: Upload macOS PR Build
         uses: actions/upload-artifact@ea165f8d65b6e75b540449e92b4886f43607fa02 # was v4
@@ -135,7 +135,7 @@ jobs:
 
       - name: Show sccache stats
         if: always()
-        run: nix develop --no-update-lock-file .#desktop-linux -c sccache --show-stats
+        run: nix develop --no-update-lock-file .#desktop-linux -c ./scripts/ci/sccache-stats.sh
 
       - name: Upload Linux PR Builds
         uses: actions/upload-artifact@ea165f8d65b6e75b540449e92b4886f43607fa02 # was v4

.github/workflows/release.yml

@@ -197,7 +197,7 @@ jobs:
 
       - name: Show sccache stats
         if: always()
-        run: nix develop --no-update-lock-file .#${{ matrix.nix_shell }} -c sccache --show-stats
+        run: nix develop --no-update-lock-file .#${{ matrix.nix_shell }} -c ./scripts/ci/sccache-stats.sh
 
       - name: Collect desktop release checksums
         run: |
@@ -434,7 +434,7 @@ jobs:
 
       - name: Show sccache stats
         if: always()
-        run: nix develop --no-update-lock-file .#android -c sccache --show-stats
+        run: nix develop --no-update-lock-file .#android -c ./scripts/ci/sccache-stats.sh
 
       - name: Collect Android release checksums
         run: |

.github/workflows/rust-tests.yml

@@ -70,4 +70,4 @@ jobs:
 
       - name: Show sccache stats
         if: always()
-        run: nix develop --no-update-lock-file .#ci -c sccache --show-stats
+        run: nix develop --no-update-lock-file .#ci -c ./scripts/ci/sccache-stats.sh

docs/repository-workflows.md

@@ -72,6 +72,12 @@ job trusts its runner with the selected environment's secrets. PR builds have
 no signing credentials and retain their existing branch-scoped caches. No
 persistent vendor disks or Docker builders are configured by these workflows.
 
+Research's Unix compiler-cache statistics use `scripts/ci/sccache-stats.sh`,
+which shares the build's cache configuration. In Actions the sccache socket
+lives under `RUNNER_TEMP`, so separate Nix shells reach the same server despite
+their different `TMPDIR` values. Cache archive restoration and compiler hits
+remain separate measurements.
+
 ## macOS runners and Apple toolchain
 
 Research desktop/iOS builds, iOS ONNX cache warming, Agent release-binary jobs

scripts/ci/_common.sh

@@ -114,7 +114,8 @@ configure_sccache() {
 
     case "${os}" in
       darwin)
-        socket_root="${TMPDIR:-/tmp}"
+        # Nix creates a different TMPDIR for each workflow step.
+        socket_root="${RUNNER_TEMP:-${TMPDIR:-/tmp}}"
         export SCCACHE_SERVER_UDS="${SCCACHE_SERVER_UDS:-${socket_root%/}/maple-sccache-${os}.sock}"
         export SCCACHE_DIR="${SCCACHE_DIR:-${HOME}/Library/Caches/Mozilla.sccache}"
         ;;
@@ -127,7 +128,7 @@ configure_sccache() {
         fi
         ;;
       *)
-        socket_root="${TMPDIR:-/tmp}"
+        socket_root="${RUNNER_TEMP:-${TMPDIR:-/tmp}}"
         export SCCACHE_SERVER_UDS="${SCCACHE_SERVER_UDS:-${socket_root%/}/maple-sccache-${os}.sock}"
         export SCCACHE_DIR="${SCCACHE_DIR:-${HOME}/.cache/sccache}"
         ;;

scripts/ci/sccache-stats.sh

@@ -0,0 +1,7 @@
+#!/usr/bin/env bash
+set -euo pipefail
+
+source "$(cd "$(dirname "${BASH_SOURCE[0]}")" && pwd)/_common.sh"
+
+configure_sccache
+exec sccache --show-stats