diff --git a/.github/actions/docker-build/action.yml b/.github/actions/docker-build/action.yml
index a607a720afd..b8727501f52 100644
--- a/.github/actions/docker-build/action.yml
+++ b/.github/actions/docker-build/action.yml
@@ -19,6 +19,13 @@ inputs:
   tags:
     description: Comma-separated list of tags to push.
     required: true
+  max-cache-size-mb:
+    description: >-
+      Layer cache to retain after the post-job prune, in MB. Must stay above one
+      build's working set (base + dependency layers + RUN --mount=type=cache
+      dirs) or every build evicts what the next one needs. Falls back to the
+      small-image default below when empty.
+    required: false
 
 # Registry logins must precede this action. provenance/sbom stay off: attestation
 # manifests break `imagetools create` retagging in promote-images.
@@ -42,11 +49,24 @@ runs:
         PLATFORMS: ${{ inputs.platforms }}
       run: echo "value=${GITHUB_REPOSITORY##*/}/${FILE#./}/${PLATFORMS//\//-}" >> "$GITHUB_OUTPUT"
 
+    # max-cache-size-mb is what bounds the disk: BuildKit's default GC is
+    # time-based only (layers unused for 8 days), and setup-docker-builder skips
+    # pruning altogether when the value is empty. On a repo that builds this
+    # often nothing ever ages out, so the disks grew without limit —
+    # app.Dockerfile/linux-amd64 reached 351 GB inside a day, and realtime, whose
+    # image is under 300 MB, sat at 249 GB. Sticky disks bill at ~$0.51/GB-month,
+    # so that was real money for layers no build would ever read again.
+    #
+    # The fallback is here rather than an input `default:` because callers pass
+    # this from a matrix field, and an unset matrix key arrives as the empty
+    # string — which counts as "provided", so a `default:` would never apply and
+    # a row that forgot the field would silently go back to unbounded growth.
     - name: Set up Blacksmith builder
       if: inputs.provider == '' || inputs.provider == 'blacksmith'
       uses: useblacksmith/setup-docker-builder@a5256a73e30f09e37e3eceb8ca36043d17621d24 # v2
       with:
         cache-key: ${{ steps.cache-key.outputs.value }}
+        max-cache-size-mb: ${{ inputs.max-cache-size-mb || '25600' }}
 
     - name: Build and push (Blacksmith)
       if: inputs.provider == '' || inputs.provider == 'blacksmith'
diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index 746c341cae8..aa1be99ea97 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -76,7 +76,7 @@ jobs:
   # (/api/desktop/update) starts offering automatically.
   detect-desktop-changes:
     name: Detect Desktop Changes
-    runs-on: blacksmith-4vcpu-ubuntu-2404
+    runs-on: ${{ (vars.CI_PROVIDER == '' || vars.CI_PROVIDER == 'blacksmith') && 'blacksmith-2vcpu-ubuntu-2404' || 'ubuntu-latest' }}
     timeout-minutes: 5
     if: github.event_name == 'push' && (github.ref == 'refs/heads/dev' || github.ref == 'refs/heads/staging')
     outputs:
@@ -165,7 +165,15 @@ jobs:
           # build` ~260s). The same `next build` runs on 16 vCPU in the separate
           # Build App verification job, which does not gate anything; this one
           # was doing comparable work on half the cores.
+          #
+          # cache_mb is the layer cache the post-job prune retains, and it is the
+          # only reason the sticky disks stay bounded — see docker-build's
+          # action.yml. Rows that omit it take the small-image default there. The
+          # app image overrides because it carries ~34 layers plus apt and bun
+          # cache mounts for the whole monorepo; 100 GB is several builds' worth
+          # of headroom over that working set.
           - dockerfile: ./docker/app.Dockerfile
+            cache_mb: '102400'
             ecr_repo_secret: ECR_APP
             gh_runner: linux-x64-8-core
             bs_runner: blacksmith-16vcpu-ubuntu-2404
@@ -176,11 +184,11 @@ jobs:
           - dockerfile: ./docker/realtime.Dockerfile
             ecr_repo_secret: ECR_REALTIME
             gh_runner: ubuntu-latest
-            bs_runner: blacksmith-4vcpu-ubuntu-2404
+            bs_runner: blacksmith-2vcpu-ubuntu-2404
           - dockerfile: ./docker/pii.Dockerfile
             ecr_repo_secret: ECR_PII
             gh_runner: ubuntu-latest
-            bs_runner: blacksmith-4vcpu-ubuntu-2404
+            bs_runner: blacksmith-2vcpu-ubuntu-2404
     steps:
       - name: Checkout code
         uses: actions/checkout@df4cb1c069e1874edd31b4311f1884172cec0e10 # v6
@@ -214,6 +222,7 @@ jobs:
           file: ${{ matrix.dockerfile }}
           platforms: linux/amd64
           tags: ${{ steps.login-ecr.outputs.registry }}/${{ steps.ecr-repo.outputs.name }}:dev
+          max-cache-size-mb: ${{ matrix.cache_mb }}
 
   # Dev: deploy Trigger.dev background tasks to the preview "dev-sim" branch.
   # Gated after migrate-dev for the same reason as build-dev — the new task
@@ -280,6 +289,7 @@ jobs:
       matrix:
         include:
           - dockerfile: ./docker/app.Dockerfile
+            cache_mb: '102400'
             ghcr_image: ghcr.io/simstudioai/simstudio
             ecr_repo_secret: ECR_APP
             gh_runner: linux-x64-8-core
@@ -293,12 +303,12 @@ jobs:
             ghcr_image: ghcr.io/simstudioai/realtime
             ecr_repo_secret: ECR_REALTIME
             gh_runner: ubuntu-latest
-            bs_runner: blacksmith-4vcpu-ubuntu-2404
+            bs_runner: blacksmith-2vcpu-ubuntu-2404
           - dockerfile: ./docker/pii.Dockerfile
             ghcr_image: ghcr.io/simstudioai/pii
             ecr_repo_secret: ECR_PII
             gh_runner: ubuntu-latest
-            bs_runner: blacksmith-4vcpu-ubuntu-2404
+            bs_runner: blacksmith-2vcpu-ubuntu-2404
           # No ECR repo is provisioned for cron, so it publishes to GHCR only.
           # The tag step below omits the ECR tag when the repo name is empty.
           - dockerfile: ./docker/cron.Dockerfile
@@ -382,6 +392,7 @@ jobs:
           file: ${{ matrix.dockerfile }}
           platforms: linux/amd64
           tags: ${{ steps.meta.outputs.tags }}
+          max-cache-size-mb: ${{ matrix.cache_mb }}
 
   # Promote the sha-tagged ECR images to the deploy tags once tests and
   # migrations pass. Pushing the ECR latest/staging tag is what triggers
@@ -484,6 +495,7 @@ jobs:
         # hang a release in `queued` rather than fail a PR.
         include:
           - dockerfile: ./docker/app.Dockerfile
+            cache_mb: '102400'
             image: ghcr.io/simstudioai/simstudio
             gh_runner: linux-arm64-8-core
             bs_runner: blacksmith-8vcpu-ubuntu-2404-arm
@@ -522,6 +534,7 @@ jobs:
           file: ${{ matrix.dockerfile }}
           platforms: linux/arm64
           tags: ${{ matrix.image }}:${{ github.sha }}-arm64
+          max-cache-size-mb: ${{ matrix.cache_mb }}
 
   # Publish all mutable GHCR tags (latest, latest-amd64/arm64, version tags)
   # and the multi-arch manifests from the immutable sha tags — only on main,
@@ -675,7 +688,7 @@ jobs:
   # Job-level `if:` cannot read the secrets context, hence the probe job.
   check-desktop-signing:
     name: Check Desktop Signing Secrets
-    runs-on: blacksmith-4vcpu-ubuntu-2404
+    runs-on: ${{ (vars.CI_PROVIDER == '' || vars.CI_PROVIDER == 'blacksmith') && 'blacksmith-2vcpu-ubuntu-2404' || 'ubuntu-latest' }}
     timeout-minutes: 2
     needs: [detect-version, detect-desktop-changes]
     # !cancelled(): detect-desktop-changes is skipped on main (and
@@ -724,7 +737,7 @@ jobs:
   # remains testable end to end with a manual download.
   create-desktop-prerelease:
     name: Create Desktop Prerelease
-    runs-on: blacksmith-4vcpu-ubuntu-2404
+    runs-on: ${{ (vars.CI_PROVIDER == '' || vars.CI_PROVIDER == 'blacksmith') && 'blacksmith-2vcpu-ubuntu-2404' || 'ubuntu-latest' }}
     timeout-minutes: 5
     needs: [detect-desktop-changes, check-desktop-signing]
     # Requires the signing probe to have actually succeeded (not just "not
@@ -813,7 +826,7 @@ jobs:
   # point of view.
   publish-desktop-prerelease:
     name: Publish Desktop Prerelease
-    runs-on: blacksmith-4vcpu-ubuntu-2404
+    runs-on: ${{ (vars.CI_PROVIDER == '' || vars.CI_PROVIDER == 'blacksmith') && 'blacksmith-2vcpu-ubuntu-2404' || 'ubuntu-latest' }}
     timeout-minutes: 5
     needs: [create-desktop-prerelease, desktop-prerelease]
     permissions:
@@ -837,7 +850,7 @@ jobs:
   # are always garbage by this point — the current run's release is published.
   prune-desktop-prereleases:
     name: Prune Desktop Prereleases
-    runs-on: blacksmith-4vcpu-ubuntu-2404
+    runs-on: ${{ (vars.CI_PROVIDER == '' || vars.CI_PROVIDER == 'blacksmith') && 'blacksmith-2vcpu-ubuntu-2404' || 'ubuntu-latest' }}
     timeout-minutes: 5
     needs: [publish-desktop-prerelease]
     permissions:
diff --git a/.github/workflows/codeql.yml b/.github/workflows/codeql.yml
index f44ca430c7c..1e7e99ce165 100644
--- a/.github/workflows/codeql.yml
+++ b/.github/workflows/codeql.yml
@@ -54,7 +54,12 @@ permissions:
 jobs:
   analyze:
     name: Analyze ${{ matrix.language }}
-    runs-on: ${{ (vars.CI_PROVIDER == '' || vars.CI_PROVIDER == 'blacksmith') && 'blacksmith-8vcpu-ubuntu-2404' || 'ubuntu-latest' }}
+    # Sized per language, not per workflow. The two analyses are nothing alike:
+    # javascript-typescript peaks at 19.5 GB (p95 over 3090 runs), so it needs
+    # the 8 vCPU tier's 30.4 GB and would OOM on the 4 vCPU tier's 15.2 GB; the
+    # actions analysis peaks at 1.3 GB and averages 22% CPU over a 39s median
+    # run, so 8 vCPU was 4x more machine than it ever used.
+    runs-on: ${{ (vars.CI_PROVIDER == '' || vars.CI_PROVIDER == 'blacksmith') && matrix.bs_runner || 'ubuntu-latest' }}
     timeout-minutes: 60
     if: github.event.pull_request.draft != true
     permissions:
@@ -71,7 +76,11 @@ jobs:
         # entries default setup listed were one analysis, not three.
         # `javascript-typescript` is the documented spelling. Python dropped:
         # 7 files in the tree.
-        language: [javascript-typescript, actions]
+        include:
+          - language: javascript-typescript
+            bs_runner: blacksmith-8vcpu-ubuntu-2404
+          - language: actions
+            bs_runner: blacksmith-4vcpu-ubuntu-2404
 
     steps:
       - name: Checkout repository