fix: reject incompatible worker architectures

[alongubkin]

Summary

• include the AWS Worker fixed arm64 requirement in release target planning
• reject Worker/x86 compute conflicts before artifact building or deployment mutation
• preserve Worker-only, compatible compute, compute-only, and non-AWS behavior

Validation

• cargo nextest run -p alien-build plan::tests --no-fail-fast (18 passed)
• git diff --check

Linear: ALIEN-920

[greptile-apps]

Confidence Score: 5/5

The PR appears safe to merge; the previous release-path validation bypass is fully fixed and no new actionable failures remain.

Summary

The PR makes release target planning account for AWS Workers’ fixed arm64 requirement and rejects incompatible Worker/compute architectures before build work begins.

• Resolves one compatible architecture across Worker and compute resources.
• Enforces the architecture contract in the shared build_stack entry point, covering release auto-builds and direct library callers.
• Adds regression coverage for Worker-only, compatible, conflicting, and early-failure paths.

Diagram

%%{init: {'theme': 'neutral'}}%%
flowchart TD
    A[Build stack] --> B[Inspect platform and resources]
    B --> C{AWS Worker present?}
    C -- Yes --> D[Require arm64]
    C -- No --> E[Resolve compute or platform architecture]
    D --> F{Compute requires x86_64?}
    F -- Yes --> G[Reject before preflights or artifacts]
    F -- No --> H[Validate requested target]
    E --> H
    H -- Mismatch --> G
    H -- Compatible --> I[Run preflights and build]

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_{Reviews (2) · Last reviewed commit: "fix: validate architecture in shared bui..."}

[alongubkin]

@greptileai review