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.github/documentation/runners.md

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+# Custom GitHub Actions Runners
+
+## Available Runners
+
+| Runner Label               | Architecture | Size   | Ephemeral | Notes                                                      |
+| -------------------------- | ------------ | ------ | --------- | ---------------------------------------------------------- |
+| `runner-small`             | x86_64       | Small  | No        | Light tasks: linting, formatting, validation               |
+| `runner-medium`            | x86_64       | Medium | No        | Standard CI: tests, builds                                 |
+| `runner-medium-arm64`      | arm64        | Medium | No        | ARM64 builds and tests                                     |
+| `runner-large`             | x86_64       | Large  | No        | Heavy workloads: benchmarks, coverage, release builds      |
+| `runner-large-spot`        | x86_64       | Large  | Yes       | Cost-optimized large jobs where interruption is acceptable |
+| `runner-medium-arm64-spot` | arm64        | Medium | Yes       | Cost-optimized ARM64 jobs where interruption is acceptable |
+
+## Spot Runners
+
+Spot runners (`*-spot`) use ephemeral cloud instances provisioned on a best-effort basis. They are significantly cheaper but can be preempted at any time if the cloud provider reclaims capacity.
+
+**Use spot runners for:**
+
+- Jobs that can be retried without consequence (test suites, linting)
+- Non-time-critical workloads
+- PR validation where re-runs are acceptable
+
+**Do not use spot runners for:**
+
+- Benchmarks (preemption and noisy-neighbor effects skew results)
+- Release builds and publishing
+- Jobs requiring consistent, reproducible timing
+
+## Choosing a Runner
+
+| Workload                        | Recommended Runner         |
+| ------------------------------- | -------------------------- |
+| Linting, formatting, validation | `runner-small`             |
+| Unit tests, standard builds     | `runner-medium`            |
+| ARM64 cross-compilation / tests | `runner-medium-arm64`      |
+| Benchmarks, coverage reports    | `runner-large`             |
+| Non-critical large builds       | `runner-large-spot`        |
+| Non-critical ARM64 builds       | `runner-medium-arm64-spot` |