diff --git a/.github/actionlint.yaml b/.github/actionlint.yaml
index bf8d62f5a1..5bef6bfac2 100644
--- a/.github/actionlint.yaml
+++ b/.github/actionlint.yaml
@@ -6,5 +6,6 @@
 # them.
 self-hosted-runner:
   labels:
-    - prod-aisimulate-default-amd64-v1
-    - prod-aisimulate-default-arm64-v1
+    - prod-aisim-default-amd64-v1
+    - prod-aisim-default-arm64-v1
+    - dynamo-cpu-4gi-amd64
diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index 5b61af95ba..0a59a481cf 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -267,11 +267,11 @@ jobs:
       matrix:
         include:
           - arch: amd64
-            runner: prod-aisimulate-default-amd64-v1
+            runner: prod-aisim-default-amd64-v1
             cargo_deny_target: x86_64-unknown-linux-musl
             cargo_deny_sha256: 0e8c2aa59128612c90d9e09c02204e912f29a5b8d9a64671b94608cbe09e064f
           - arch: arm64
-            runner: prod-aisimulate-default-arm64-v1
+            runner: prod-aisim-default-arm64-v1
             cargo_deny_target: aarch64-unknown-linux-musl
             cargo_deny_sha256: 2b3567a60b7491c159d1cef8b7d8479d1ad2a31e29ef49462634ad4552fcc77d
     runs-on: ${{ matrix.runner }}
@@ -279,7 +279,7 @@ jobs:
     container:
       image: ${{ vars.CI_JOB_CONTAINER_IMAGE }}
       env:
-        HOME: ${{ github.workspace }}
+        HOME: /__w/aisim/aisim
         USER: runner
     steps:
       - uses: actions/checkout@3d3c42e5aac5ba805825da76410c181273ba90b1 # v7
@@ -316,11 +316,11 @@ jobs:
       fail-fast: false
       matrix:
         arch: [amd64, arm64]
-    runs-on: prod-aisimulate-default-${{ matrix.arch }}-v1
+    runs-on: prod-aisim-default-${{ matrix.arch }}-v1
     container:
       image: ${{ vars.CI_JOB_CONTAINER_IMAGE }}
       env:
-        HOME: ${{ github.workspace }}
+        HOME: /__w/aisim/aisim
         USER: runner
     steps:
       - uses: actions/checkout@3d3c42e5aac5ba805825da76410c181273ba90b1 # v7
@@ -335,14 +335,14 @@ jobs:
     name: Rust feature modes
     needs: [fast-ci, select-full-ci]
     if: ${{ needs.select-full-ci.outputs.rust_feature_modes == 'true' }}
-    runs-on: prod-aisimulate-default-amd64-v1
+    runs-on: prod-aisim-default-amd64-v1
     timeout-minutes: 15
     env:
       CARGO_TARGET_DIR: ${{ github.workspace }}/target-feature-tests
     container:
       image: ${{ vars.CI_JOB_CONTAINER_IMAGE }}
       env:
-        HOME: ${{ github.workspace }}
+        HOME: /__w/aisim/aisim
         USER: runner
     steps:
       - uses: actions/checkout@3d3c42e5aac5ba805825da76410c181273ba90b1 # v7
@@ -381,11 +381,11 @@ jobs:
       fail-fast: false
       matrix:
         arch: [amd64, arm64]
-    runs-on: prod-aisimulate-default-${{ matrix.arch }}-v1
+    runs-on: prod-aisim-default-${{ matrix.arch }}-v1
     container:
       image: ${{ vars.CI_JOB_CONTAINER_IMAGE }}
       env:
-        HOME: ${{ github.workspace }}
+        HOME: /__w/aisim/aisim
         USER: runner
     steps:
       - uses: actions/checkout@3d3c42e5aac5ba805825da76410c181273ba90b1 # v7
@@ -412,11 +412,11 @@ jobs:
       fail-fast: false
       matrix:
         arch: [amd64, arm64]
-    runs-on: prod-aisimulate-default-${{ matrix.arch }}-v1
+    runs-on: prod-aisim-default-${{ matrix.arch }}-v1
     container:
       image: ${{ vars.CI_JOB_CONTAINER_IMAGE }}
       env:
-        HOME: ${{ github.workspace }}
+        HOME: /__w/aisim/aisim
         USER: runner
     steps:
       - uses: actions/checkout@3d3c42e5aac5ba805825da76410c181273ba90b1 # v7
@@ -461,11 +461,11 @@ jobs:
       fail-fast: false
       matrix:
         arch: [amd64, arm64]
-    runs-on: prod-aisimulate-default-${{ matrix.arch }}-v1
+    runs-on: prod-aisim-default-${{ matrix.arch }}-v1
     container:
       image: ${{ vars.CI_JOB_CONTAINER_IMAGE }}
       env:
-        HOME: ${{ github.workspace }}
+        HOME: /__w/aisim/aisim
         USER: runner
     steps:
       - uses: actions/download-artifact@3e5f45b2cfb9172054b4087a40e8e0b5a5461e7c # v8.0.1
@@ -600,12 +600,12 @@ jobs:
           - arch: arm64
             # quay.io/pypa/manylinux_2_28_aarch64:2026.08.24-1
             container_image: quay.io/pypa/manylinux_2_28_aarch64@sha256:29a6ceb78de5b00494e6e7456a72782a4cb54238de102e7491d15fe47789b4d1
-    runs-on: prod-aisimulate-default-${{ matrix.arch }}-v1
+    runs-on: prod-aisim-default-${{ matrix.arch }}-v1
     timeout-minutes: 10
     container:
       image: ${{ matrix.container_image }}
       env:
-        HOME: ${{ github.workspace }}
+        HOME: /__w/aisim/aisim
         USER: runner
     steps:
       - uses: actions/checkout@3d3c42e5aac5ba805825da76410c181273ba90b1 # v7
@@ -655,12 +655,12 @@ jobs:
           - {suite: cli-build, group: 4, groups: 4}
           - {suite: support-matrix, group: 1, groups: 1}
           - {suite: tools-build, group: 1, groups: 1}
-    runs-on: prod-aisimulate-default-${{ matrix.arch }}-v1
+    runs-on: prod-aisim-default-${{ matrix.arch }}-v1
     timeout-minutes: 15
     container:
       image: ${{ vars.CI_JOB_CONTAINER_IMAGE }}
       env:
-        HOME: ${{ github.workspace }}
+        HOME: /__w/aisim/aisim
         USER: runner
     steps:
       - uses: actions/checkout@3d3c42e5aac5ba805825da76410c181273ba90b1 # v7
@@ -776,12 +776,12 @@ jobs:
         needs.select-full-ci.result == 'success' &&
         needs.select-full-ci.outputs.application_wheel == 'true'
       }}
-    runs-on: prod-aisimulate-default-amd64-v1
+    runs-on: prod-aisim-default-amd64-v1
     timeout-minutes: 15
     container:
       image: ${{ vars.CI_JOB_CONTAINER_IMAGE }}
       env:
-        HOME: ${{ github.workspace }}
+        HOME: /__w/aisim/aisim
         USER: runner
     steps:
       - uses: actions/checkout@3d3c42e5aac5ba805825da76410c181273ba90b1 # v7
@@ -798,7 +798,7 @@ jobs:
     name: Python ${{ matrix.python-version }} compatibility
     needs: [fast-ci, select-full-ci]
     if: ${{ needs.select-full-ci.outputs.python_compatibility == 'true' }}
-    runs-on: prod-aisimulate-default-amd64-v1
+    runs-on: prod-aisim-default-amd64-v1
     timeout-minutes: 30
     strategy:
       fail-fast: false
@@ -807,7 +807,7 @@ jobs:
     container:
       image: ${{ vars.CI_JOB_CONTAINER_IMAGE }}
       env:
-        HOME: ${{ github.workspace }}
+        HOME: /__w/aisim/aisim
         USER: runner
     steps:
       - uses: actions/checkout@3d3c42e5aac5ba805825da76410c181273ba90b1 # v7
@@ -831,12 +831,12 @@ jobs:
     name: Engine Golden Regression
     needs: [fast-ci, select-full-ci]
     if: ${{ needs.select-full-ci.outputs.engine_golden_regression == 'true' }}
-    runs-on: prod-aisimulate-default-amd64-v1
+    runs-on: prod-aisim-default-amd64-v1
     timeout-minutes: 45
     container:
       image: ${{ vars.CI_JOB_CONTAINER_IMAGE }}
       env:
-        HOME: ${{ github.workspace }}
+        HOME: /__w/aisim/aisim
         USER: runner
     steps:
       - uses: actions/checkout@3d3c42e5aac5ba805825da76410c181273ba90b1 # v7
@@ -886,11 +886,11 @@ jobs:
           - arch: arm64
             # quay.io/pypa/manylinux_2_28_aarch64:2026.08.24-1
             container_image: quay.io/pypa/manylinux_2_28_aarch64@sha256:29a6ceb78de5b00494e6e7456a72782a4cb54238de102e7491d15fe47789b4d1
-    runs-on: prod-aisimulate-default-${{ matrix.arch }}-v1
+    runs-on: prod-aisim-default-${{ matrix.arch }}-v1
     container:
       image: ${{ matrix.container_image }}
       env:
-        HOME: ${{ github.workspace }}
+        HOME: /__w/aisim/aisim
         USER: runner
     steps:
       - uses: actions/checkout@3d3c42e5aac5ba805825da76410c181273ba90b1 # v7
diff --git a/.github/workflows/collector-check.yml b/.github/workflows/collector-check.yml
index 51e9ff46ce..46533822b4 100644
--- a/.github/workflows/collector-check.yml
+++ b/.github/workflows/collector-check.yml
@@ -26,12 +26,12 @@ concurrency:
 jobs:
   check:
     name: Check collector data
-    runs-on: prod-aisimulate-default-amd64-v1
+    runs-on: prod-aisim-default-amd64-v1
     timeout-minutes: 20
     container:
       image: ${{ vars.CI_JOB_CONTAINER_IMAGE }}
       env:
-        HOME: ${{ github.workspace }}
+        HOME: /__w/aisim/aisim
         USER: runner
     steps:
       - name: Checkout code
@@ -57,13 +57,13 @@ jobs:
 
   cross-backend-consistency:
     name: Perf data sanity (informational)
-    runs-on: prod-aisimulate-default-amd64-v1
+    runs-on: prod-aisim-default-amd64-v1
     timeout-minutes: 25
     continue-on-error: true
     container:
       image: ${{ vars.CI_JOB_CONTAINER_IMAGE }}
       env:
-        HOME: ${{ github.workspace }}
+        HOME: /__w/aisim/aisim
         USER: runner
     steps:
       - name: Checkout code
diff --git a/.github/workflows/e2e-accuracy-branch.yml b/.github/workflows/e2e-accuracy-branch.yml
index edf3de6db6..89982b0fea 100644
--- a/.github/workflows/e2e-accuracy-branch.yml
+++ b/.github/workflows/e2e-accuracy-branch.yml
@@ -45,7 +45,7 @@ permissions:
 jobs:
   wheel:
     name: Prepare exact accuracy wheel
-    runs-on: prod-aisimulate-default-amd64-v1
+    runs-on: prod-aisim-default-amd64-v1
     timeout-minutes: 120
     permissions:
       contents: read
@@ -135,11 +135,11 @@ jobs:
   measurements:
     name: Prepare shared E2E measurements
     timeout-minutes: 120
-    runs-on: prod-aisimulate-default-amd64-v1
+    runs-on: prod-aisim-default-amd64-v1
     container:
       image: ${{ vars.CI_JOB_CONTAINER_IMAGE }}
       env:
-        HOME: ${{ github.workspace }}
+        HOME: /__w/aisim/aisim
         USER: runner
     steps:
       - uses: actions/checkout@3d3c42e5aac5ba805825da76410c181273ba90b1 # v7
@@ -189,13 +189,13 @@ jobs:
       max-parallel: 4
       matrix:
         shard: [0, 1, 2, 3]
-    runs-on: prod-aisimulate-default-amd64-v1
+    runs-on: prod-aisim-default-amd64-v1
     timeout-minutes: 360
     container:
       # The runner executes as non-root; use its sudo-enabled CI image.
       image: ${{ vars.CI_JOB_CONTAINER_IMAGE }}
       env:
-        HOME: ${{ github.workspace }}
+        HOME: /__w/aisim/aisim
         USER: runner
     env:
       OPENBLAS_NUM_THREADS: '1'
@@ -313,11 +313,11 @@ jobs:
     name: Qualify E2E accuracy (${{ inputs.artifact_key }})
     needs: [wheel, shards]
     timeout-minutes: 30
-    runs-on: prod-aisimulate-default-amd64-v1
+    runs-on: prod-aisim-default-amd64-v1
     container:
       image: ${{ vars.CI_JOB_CONTAINER_IMAGE }}
       env:
-        HOME: ${{ github.workspace }}
+        HOME: /__w/aisim/aisim
         USER: runner
     steps:
       - uses: actions/checkout@3d3c42e5aac5ba805825da76410c181273ba90b1 # v7
@@ -397,12 +397,12 @@ jobs:
       max-parallel: 2
       matrix:
         shard: [0, 1]
-    runs-on: prod-aisimulate-default-amd64-v1
+    runs-on: prod-aisim-default-amd64-v1
     timeout-minutes: 360
     container:
       image: ${{ vars.CI_JOB_CONTAINER_IMAGE }}
       env:
-        HOME: ${{ github.workspace }}
+        HOME: /__w/aisim/aisim
         USER: runner
     env:
       OPENBLAS_NUM_THREADS: '1'
@@ -485,12 +485,12 @@ jobs:
   qualify-agentx:
     name: Qualify AgentX accuracy (${{ inputs.artifact_key }})
     needs: agentx
-    runs-on: prod-aisimulate-default-amd64-v1
+    runs-on: prod-aisim-default-amd64-v1
     timeout-minutes: 30
     container:
       image: ${{ vars.CI_JOB_CONTAINER_IMAGE }}
       env:
-        HOME: ${{ github.workspace }}
+        HOME: /__w/aisim/aisim
         USER: runner
     steps:
       - uses: actions/checkout@3d3c42e5aac5ba805825da76410c181273ba90b1 # v7
diff --git a/.github/workflows/fpe-release-qualify.yml b/.github/workflows/fpe-release-qualify.yml
index 79730ec4eb..2e66255b70 100644
--- a/.github/workflows/fpe-release-qualify.yml
+++ b/.github/workflows/fpe-release-qualify.yml
@@ -26,7 +26,7 @@ jobs:
   prepare:
     name: Build and identify release FPE wheel
     if: github.ref == 'refs/heads/main'
-    runs-on: prod-aisimulate-default-amd64-v1
+    runs-on: prod-aisim-default-amd64-v1
     timeout-minutes: 30
     container:
       # Same pinned manylinux toolchain as the main FPE producer.
@@ -75,7 +75,7 @@ jobs:
   generate:
     name: Release FPE (${{ matrix.shard.system }}, ${{ matrix.shard.backend }})
     needs: prepare
-    runs-on: prod-aisimulate-default-amd64-v1
+    runs-on: prod-aisim-default-amd64-v1
     timeout-minutes: 480
     container:
       image: ${{ vars.CI_JOB_CONTAINER_IMAGE }}
diff --git a/.github/workflows/fpe-support-matrix.yml b/.github/workflows/fpe-support-matrix.yml
index ceda22708c..7bb02e64ec 100644
--- a/.github/workflows/fpe-support-matrix.yml
+++ b/.github/workflows/fpe-support-matrix.yml
@@ -35,13 +35,13 @@ env:
 jobs:
   prepare-wheel:
     name: Prepare exact FPE wheel
-    runs-on: prod-aisimulate-default-amd64-v1
+    runs-on: prod-aisim-default-amd64-v1
     timeout-minutes: 30
     container:
       # quay.io/pypa/manylinux_2_28_x86_64:2026.08.24-1
       image: quay.io/pypa/manylinux_2_28_x86_64@sha256:4dc41da7df20400310c80d162a2fe2d2c2f3d9734d8dec20f6b9843711618deb
       env:
-        HOME: ${{ github.workspace }}
+        HOME: /__w/aisim/aisim
         USER: runner
     outputs:
       wheel-sha256: ${{ steps.digest.outputs.sha256 }}
@@ -150,12 +150,12 @@ jobs:
   generate:
     name: FPE matrix (${{ matrix.shard.system }}, ${{ matrix.shard.backend }})
     needs: [discover-shards, prepare-wheel]
-    runs-on: prod-aisimulate-default-amd64-v1
+    runs-on: prod-aisim-default-amd64-v1
     timeout-minutes: 480
     container:
       image: ${{ vars.CI_JOB_CONTAINER_IMAGE }}
       env:
-        HOME: ${{ github.workspace }}
+        HOME: /__w/aisim/aisim
         USER: runner
     strategy:
       fail-fast: false
diff --git a/.github/workflows/fpm-accuracy-branch.yml b/.github/workflows/fpm-accuracy-branch.yml
index 6c8c28e288..7a3f5f9426 100644
--- a/.github/workflows/fpm-accuracy-branch.yml
+++ b/.github/workflows/fpm-accuracy-branch.yml
@@ -29,7 +29,7 @@ permissions:
 jobs:
   wheel:
     name: Prepare exact accuracy wheel
-    runs-on: prod-aisimulate-default-amd64-v1
+    runs-on: prod-aisim-default-amd64-v1
     timeout-minutes: 120
     permissions:
       contents: read
@@ -119,7 +119,7 @@ jobs:
   campaign:
     name: Qualify FPM accuracy (${{ inputs.artifact_key }})
     needs: wheel
-    runs-on: prod-aisimulate-default-amd64-v1
+    runs-on: prod-aisim-default-amd64-v1
     timeout-minutes: 360
     container:
       image: quay.io/pypa/manylinux_2_28_x86_64@sha256:4dc41da7df20400310c80d162a2fe2d2c2f3d9734d8dec20f6b9843711618deb
diff --git a/.github/workflows/nightly-ci.yml b/.github/workflows/nightly-ci.yml
index 225fe691d7..0dfb11bfba 100644
--- a/.github/workflows/nightly-ci.yml
+++ b/.github/workflows/nightly-ci.yml
@@ -292,12 +292,12 @@ jobs:
       matrix:
         arch: [amd64, arm64]
         python-version: ["3.11", "3.12", "3.13"]
-    runs-on: prod-aisimulate-default-${{ matrix.arch }}-v1
+    runs-on: prod-aisim-default-${{ matrix.arch }}-v1
     timeout-minutes: 15
     container:
       image: ${{ vars.CI_JOB_CONTAINER_IMAGE }}
       env:
-        HOME: ${{ github.workspace }}
+        HOME: /__w/aisim/aisim
         USER: runner
     steps:
       # Keep the license policy/tooling at the workflow revision. Older
@@ -351,7 +351,7 @@ jobs:
       matrix:
         include:
           - arch: amd64
-            runner: prod-aisimulate-default-amd64-v1
+            runner: prod-aisim-default-amd64-v1
             rust_target: x86_64-unknown-linux-gnu
             rustup_init_sha256: 4acc9acc76d5079515b46346a485974457b5a79893cfb01112423c89aeb5aa10
             uv_target: x86_64-unknown-linux-gnu
@@ -359,7 +359,7 @@ jobs:
             # quay.io/pypa/manylinux_2_28_x86_64:2026.08.24-1
             container_image: quay.io/pypa/manylinux_2_28_x86_64@sha256:4dc41da7df20400310c80d162a2fe2d2c2f3d9734d8dec20f6b9843711618deb
           - arch: arm64
-            runner: prod-aisimulate-default-arm64-v1
+            runner: prod-aisim-default-arm64-v1
             rust_target: aarch64-unknown-linux-gnu
             rustup_init_sha256: 9732d6c5e2a098d3521fca8145d826ae0aaa067ef2385ead08e6feac88fa5792
             uv_target: aarch64-unknown-linux-gnu
@@ -380,7 +380,7 @@ jobs:
       # for the runner's node24-based actions.
       image: ${{ matrix.container_image }}
       env:
-        HOME: ${{ github.workspace }}
+        HOME: /__w/aisim/aisim
     defaults:
       run:
         shell: bash
diff --git a/.github/workflows/performance.yml b/.github/workflows/performance.yml
index 1ad3e51217..1dc12ed878 100644
--- a/.github/workflows/performance.yml
+++ b/.github/workflows/performance.yml
@@ -53,7 +53,7 @@ jobs:
     needs: select
     if: needs.select.outputs.run_comparison == 'true'
     name: Forward Prediction Performance (advisory)
-    runs-on: prod-aisimulate-default-amd64-v1
+    runs-on: prod-aisim-default-amd64-v1
     timeout-minutes: 45
     defaults:
       run:
@@ -61,7 +61,7 @@ jobs:
     container:
       image: ${{ vars.CI_JOB_CONTAINER_IMAGE }}
       env:
-        HOME: ${{ github.workspace }}
+        HOME: /__w/aisim/aisim
         USER: runner
     steps:
       - uses: actions/checkout@3d3c42e5aac5ba805825da76410c181273ba90b1 # v7.0.1
diff --git a/.github/workflows/prediction-regression-gate.yml b/.github/workflows/prediction-regression-gate.yml
index f65a9b58be..bbe794cce4 100644
--- a/.github/workflows/prediction-regression-gate.yml
+++ b/.github/workflows/prediction-regression-gate.yml
@@ -56,7 +56,7 @@ jobs:
   collect:
     name: Collect prediction snapshot (${{ matrix.side }})
     needs: refs
-    runs-on: prod-aisimulate-default-amd64-v1
+    runs-on: prod-aisim-default-amd64-v1
     timeout-minutes: 45
     strategy:
       fail-fast: false
@@ -65,7 +65,7 @@ jobs:
     container:
       image: ${{ vars.CI_JOB_CONTAINER_IMAGE }}
       env:
-        HOME: ${{ github.workspace }}
+        HOME: /__w/aisim/aisim
         USER: runner
     steps:
       - name: Checkout comparison revision
diff --git a/.github/workflows/runner-canary.yml b/.github/workflows/runner-canary.yml
new file mode 100644
index 0000000000..fa17cbbf64
--- /dev/null
+++ b/.github/workflows/runner-canary.yml
@@ -0,0 +1,80 @@
+# SPDX-FileCopyrightText: Copyright (c) 2026 NVIDIA CORPORATION & AFFILIATES. All rights reserved.
+# SPDX-License-Identifier: Apache-2.0
+# Keep normal producers paused until this smoke matrix passes.
+name: Runner canary
+
+on:
+  workflow_dispatch:
+  push:
+    branches: ["pull-request/*"]
+    paths: [".github/workflows/runner-canary.yml"]
+
+permissions:
+  contents: read
+
+jobs:
+  canary:
+    if: github.repository == 'ai-dynamo/aisim'
+    name: Runner canary (${{ matrix.pool }})
+    strategy:
+      fail-fast: false
+      matrix:
+        include:
+          - pool: amd64
+            runner: prod-aisim-default-amd64-v1
+            machine: x86_64
+            scratch: true
+          - pool: arm64
+            runner: prod-aisim-default-arm64-v1
+            machine: aarch64
+            scratch: true
+    runs-on: ${{ matrix.runner }}
+    timeout-minutes: 10
+    container:
+      image: ${{ vars.CI_JOB_CONTAINER_IMAGE }}
+      env:
+        HOME: /__w/aisim/aisim
+        USER: runner
+    steps:
+      - uses: actions/checkout@3d3c42e5aac5ba805825da76410c181273ba90b1 # v7
+      - name: Verify source, job workspace, architecture and storage
+        shell: bash
+        env:
+          EXPECTED_MACHINE: ${{ matrix.machine }}
+          EXPECT_SCRATCH: ${{ matrix.scratch }}
+        run: |
+          set -euo pipefail
+          test "${GITHUB_REPOSITORY}" = ai-dynamo/aisim
+          test "$(git rev-parse HEAD)" = "${GITHUB_SHA}"
+          test "$(pwd -P)" = /__w/aisim/aisim
+          test "${HOME}" = /__w/aisim/aisim
+          test -w "${HOME}"
+          test "$(uname -m)" = "${EXPECTED_MACHINE}"
+          probe=$(mktemp "${HOME}/.runner-canary.XXXXXX")
+          rm "${probe}"
+          if [[ "${EXPECT_SCRATCH}" == true ]]; then
+            test -w /scratch
+            probe=$(mktemp /scratch/runner-canary.XXXXXX)
+            rm "${probe}"
+          fi
+          printf 'Verified source %s on %s (%s) with writable HOME=%s\n' "${GITHUB_SHA}" "${RUNNER_NAME}" "${EXPECTED_MACHINE}" "${HOME}"
+
+  shared:
+    if: github.repository == 'ai-dynamo/aisim'
+    name: Runner canary (shared)
+    runs-on: dynamo-cpu-4gi-amd64
+    timeout-minutes: 10
+    steps:
+      - uses: actions/checkout@3d3c42e5aac5ba805825da76410c181273ba90b1 # v7
+      - name: Verify shared runner admission, source and writable workspace
+        shell: bash
+        run: |
+          set -euo pipefail
+          test "${GITHUB_REPOSITORY}" = ai-dynamo/aisim
+          test "$(git rev-parse HEAD)" = "${GITHUB_SHA}"
+          test "$(pwd -P)" = "$(realpath "${GITHUB_WORKSPACE}")"
+          test "$(uname -m)" = x86_64
+          test -w "${HOME}"
+          probe=$(mktemp .runner-canary.XXXXXX)
+          rm "${probe}"
+          printf 'Verified source %s on shared runner %s\n' "${GITHUB_SHA}" "${RUNNER_NAME}"
diff --git a/.github/workflows/simulation-performance.yml b/.github/workflows/simulation-performance.yml
index 8ffe65a472..6b7ca3174b 100644
--- a/.github/workflows/simulation-performance.yml
+++ b/.github/workflows/simulation-performance.yml
@@ -165,7 +165,7 @@ jobs:
     needs: select
     if: needs.select.outputs.run_comparison == 'true'
     name: Build simulation wheel (${{ matrix.side }})
-    runs-on: prod-aisimulate-default-amd64-v1
+    runs-on: prod-aisim-default-amd64-v1
     timeout-minutes: 30
     strategy:
       fail-fast: false
@@ -181,7 +181,7 @@ jobs:
     container:
       image: ${{ vars.CI_JOB_CONTAINER_IMAGE }}
       env:
-        HOME: ${{ github.workspace }}
+        HOME: /__w/aisim/aisim
         USER: runner
     steps:
       - uses: actions/checkout@3d3c42e5aac5ba805825da76410c181273ba90b1 # v7.0.1
@@ -260,7 +260,7 @@ jobs:
     needs: [select, build]
     if: needs.select.outputs.run_comparison == 'true'
     name: Simulation Performance (advisory)
-    runs-on: prod-aisimulate-default-amd64-v1
+    runs-on: prod-aisim-default-amd64-v1
     timeout-minutes: 75
     defaults:
       run:
@@ -268,7 +268,7 @@ jobs:
     container:
       image: ${{ vars.CI_JOB_CONTAINER_IMAGE }}
       env:
-        HOME: ${{ github.workspace }}
+        HOME: /__w/aisim/aisim
         USER: runner
     env:
       BASE_SHA: ${{ needs.select.outputs.base_sha }}
diff --git a/docs/perf-model/configuration.md b/docs/perf-model/configuration.md
index a4d4d1976e..229f58d000 100644
--- a/docs/perf-model/configuration.md
+++ b/docs/perf-model/configuration.md
@@ -1398,12 +1398,16 @@ work as before in this release. The next release removes them.
 | `engine.estimation_mode` | `auto` | `x` | `-` | Deprecated; use [`engine.ais_perf_model`](#unified-perf-model-input). `auto`, `op_level`, `fpm_interpolation`, `fpm_regression`, or `fpm_learned`. Regression and learned roles are priced per iteration (see [engine replay timing](#engine-replay-timing)). |
 | `engine.workers.<role>.timing.estimation_mode` | `null` | `x` | `-` | Deprecated; use [`engine.ais_perf_model`](#unified-perf-model-input). Optional role override using the same five modes; omission inherits the global selection. |
 | `engine.workers.<role>.timing.type` | `default` | `x` | `-` | `default`, `fixed`, or `polynomial`. |
-| `engine.workers.<role>.timing.prefill_ms` | `null` | `x` | `-` | Nonnegative and required for `fixed` timing. |
-| `engine.workers.<role>.timing.decode_ms` | `null` | `x` | `-` | Nonnegative and required for `fixed` timing. |
+| `engine.workers.<role>.timing.prefill_ms` | `null` | `x` | `-` | Finite, nonnegative and required for `fixed` timing. |
+| `engine.workers.<role>.timing.decode_ms` | `null` | `x` | `-` | Finite, nonnegative and required for `fixed` timing. |
 | `engine.workers.<role>.timing.forward_model` | `op_level` | `x` | `-` | Deprecated; use [`engine.ais_perf_model`](#unified-perf-model-input). `op_level` or `fpm`; `default` timing only. `fpm` replays whole-forward (FPM) latency measured for the role's exact model, hardware, backend version, parallel shape and quantization, and fails closed when no such cell exists. |
 | `engine.workers.<role>.timing.fpm_parquet_path` | `null` | `x` | `-` | Deprecated; use [`engine.ais_perf_model`](#unified-perf-model-input). External FPM parquet for `forward_model: fpm`; the adjacent same-stem `.metadata.json` sidecar is required. Relative paths are anchored to the working directory when the engine is constructed. Preserved per role in recommendations, candidate YAML, and ordinary prefill/decode companions of AFD roles. |
 | `engine.workers.<role>.timing.estimator_config.state_snapshot` | `null` | `x` | `-` | Deprecated; use [`engine.ais_perf_model`](#unified-perf-model-input). `recommend`: `{path, sha256}` of a calibrated snapshot; the role takes its estimator and engine identity from it. See [snapshot roles](#recommending-with-a-calibrated-snapshot). `predict` requires the complete saved configuration, as for any `state_snapshot`. |
 
+Fixed timing accepts zero for either phase. Nonfinite values (infinity or NaN)
+are configuration errors, rejected before prediction output is prepared, including
+when `--overwrite` is used.
+
 AFD replay prices every decode pass at its actual batch, context length and
 MTP verification width. The former `estimator_config.afd.frozen_decode_identity`
 control and saved pricing identity have been removed. Configurations and saved
diff --git a/python/aisim/src/aisim/config/engine.py b/python/aisim/src/aisim/config/engine.py
index cbae5529d0..0ccc942e1f 100644
--- a/python/aisim/src/aisim/config/engine.py
+++ b/python/aisim/src/aisim/config/engine.py
@@ -501,8 +501,8 @@ def _preserve_legacy_estimator_selection(cls, value):
                 value.setdefault("fallback_policy", "deny")
         return value
 
-    prefill_ms: float | None = Field(default=None, ge=0.0)
-    decode_ms: float | None = Field(default=None, ge=0.0)
+    prefill_ms: float | None = Field(default=None, ge=0.0, allow_inf_nan=False)
+    decode_ms: float | None = Field(default=None, ge=0.0, allow_inf_nan=False)
 
     @model_validator(mode="after")
     def _validate_timing(self) -> TimingConfig: