ci: improve go caches (#38730)

Cache saves have been rejected since June because the repo sat above its
10 GB allowance, so every PR run fell back to a cache built with an
older toolchain and rebuilt the backend from scratch.

- go version in the `gobuild` and `golint` keys and `restore-keys`
- seeder triggers on `go.mod` and gained `workflow_dispatch`
- single writer for the `gomod` cache, the two were racing
- new daily `cache-prune` workflow holding the total under a limit
- `cache: false` for `setup-go` in release and cron workflows, it held
815 MB
- add `workflow_dispatch` so the cache workflows can be triggered
on-demand

Assisted-by: Claude Code:claude-opus-5

.github/actions/go-cache/action.yml

@@ -2,12 +2,18 @@ name: go-caches
 description: Restore the go module, build, and golangci-lint caches. Save only on the cache-seeder workflow.
 
 # Only the cache-seeder workflow saves; rename requires updating cache-seeder.yml.
-# The lint job restores but does not save the gobuild cache, so only one writer
-# (the gobuild job) populates it and there is no contention on the cache key.
+# The lint job restores but does not save the gobuild and gomod caches, so every key
+# has a single writer and there is no contention on it.
 # Seeder restores by exact key only (no restore-keys) so each go.sum seeds a clean
 # cache and size stays bounded; do not add restore-keys here. PR runs keep them.
+# The go version is part of the gobuild and golint keys because a toolchain bump
+# invalidates every entry in them, so a cross-version fallback would restore
+# gigabytes that no build can use. The module cache is version-independent.
 
 inputs:
+  go-version:
+    description: Go version the build caches belong to
+    required: true
   lint-cache:
     description: Restore (and save in cache-seeder) ~/.cache/golangci-lint
     default: "false"
@@ -15,12 +21,12 @@ inputs:
 runs:
   using: composite
   steps:
-    - if: ${{ github.workflow == 'cache-seeder' }}
+    - if: ${{ github.workflow == 'cache-seeder' && inputs.lint-cache != 'true' }}
       uses: actions/cache@55cc8345863c7cc4c66a329aec7e433d2d1c52a9 # v6.1.0
       with:
         path: ~/go/pkg/mod
         key: gomod-${{ runner.os }}-${{ runner.arch }}-${{ hashFiles('go.sum') }}
-    - if: ${{ github.workflow != 'cache-seeder' }}
+    - if: ${{ github.workflow != 'cache-seeder' || inputs.lint-cache == 'true' }}
       uses: actions/cache/restore@55cc8345863c7cc4c66a329aec7e433d2d1c52a9 # v6.1.0
       with:
         path: ~/go/pkg/mod
@@ -30,21 +36,21 @@ runs:
       uses: actions/cache@55cc8345863c7cc4c66a329aec7e433d2d1c52a9 # v6.1.0
       with:
         path: ~/.cache/go-build
-        key: gobuild-${{ runner.os }}-${{ runner.arch }}-${{ hashFiles('go.sum') }}
+        key: gobuild-${{ runner.os }}-${{ runner.arch }}-go${{ inputs.go-version }}-${{ hashFiles('go.sum') }}
     - if: ${{ github.workflow != 'cache-seeder' || inputs.lint-cache == 'true' }}
       uses: actions/cache/restore@55cc8345863c7cc4c66a329aec7e433d2d1c52a9 # v6.1.0
       with:
         path: ~/.cache/go-build
-        key: gobuild-${{ runner.os }}-${{ runner.arch }}-${{ hashFiles('go.sum') }}
-        restore-keys: gobuild-${{ runner.os }}-${{ runner.arch }}
+        key: gobuild-${{ runner.os }}-${{ runner.arch }}-go${{ inputs.go-version }}-${{ hashFiles('go.sum') }}
+        restore-keys: gobuild-${{ runner.os }}-${{ runner.arch }}-go${{ inputs.go-version }}-
     - if: ${{ inputs.lint-cache == 'true' && github.workflow == 'cache-seeder' }}
       uses: actions/cache@55cc8345863c7cc4c66a329aec7e433d2d1c52a9 # v6.1.0
       with:
         path: ~/.cache/golangci-lint
-        key: golint-${{ runner.os }}-${{ runner.arch }}-${{ hashFiles('go.sum', '.golangci.yml') }}
+        key: golint-${{ runner.os }}-${{ runner.arch }}-go${{ inputs.go-version }}-${{ hashFiles('go.sum', '.golangci.yml') }}
     - if: ${{ inputs.lint-cache == 'true' && github.workflow != 'cache-seeder' }}
       uses: actions/cache/restore@55cc8345863c7cc4c66a329aec7e433d2d1c52a9 # v6.1.0
       with:
         path: ~/.cache/golangci-lint
-        key: golint-${{ runner.os }}-${{ runner.arch }}-${{ hashFiles('go.sum', '.golangci.yml') }}
-        restore-keys: golint-${{ runner.os }}-${{ runner.arch }}
+        key: golint-${{ runner.os }}-${{ runner.arch }}-go${{ inputs.go-version }}-${{ hashFiles('go.sum', '.golangci.yml') }}
+        restore-keys: golint-${{ runner.os }}-${{ runner.arch }}-go${{ inputs.go-version }}-

.github/actions/go-setup/action.yml

@@ -14,6 +14,7 @@ runs:
   steps:
     - uses: ./.github/actions/free-disk-space
     - uses: actions/setup-go@b7ad1dad31e06c5925ef5d2fc7ad053ef454303e # v7
+      id: setup-go
       with:
         go-version-file: go.mod
         check-latest: true
@@ -21,4 +22,5 @@ runs:
     - if: ${{ inputs.cache == 'true' }}
       uses: ./.github/actions/go-cache
       with:
+        go-version: ${{ steps.setup-go.outputs.go-version }}
         lint-cache: ${{ inputs.lint-cache }}