Fix Railway Docker cache-mount build failures

[BigSimmo]

Summary

• remove Railway-incompatible BuildKit cache mounts from both production Dockerfiles
• preserve install retries, pinned base images, image hardening, and runtime validation
• add regression coverage preventing service-ID-coupled cache mounts from returning
• keep GitHub's optional Buildx cache non-blocking and cap cache waits at two minutes
• align deployment documentation with the portable image contract

Root cause

PR #1575 added --mount=type=cache directives using standard Docker syntax. Railway applies a stricter cache-ID contract and rejects these Dockerfiles during early build validation. PR #1596 added bare worker IDs, but Railway then rejected them for lacking its required cache-key prefix. PR #1597 remains worker-only and still does not fix the app Dockerfile.

Railway requires cache IDs to contain a hard-coded Railway service ID and does not allow an environment variable for that portion. Because this repository builds shared images in CI and deploys them to separate Railway services, removing the optional mounts is the smallest portable fix.

Verification

• regression contract: red before the fix, green after it
• app image: built and passed provider-free container smoke
• worker image: built and passed network-isolated runtime validation
• image-content and read-only runtime contracts: passed
• unit coverage, static checks, safety/config, application build, Lighthouse: passed
• SAST and secret scanning: passed
• required PR aggregate: passed

No provider data, secrets, database schema, dependency versions, or runtime behavior changed.

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Review details

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Run ID: 764f8559-d008-4460-be98-357d41e28b5b

📥 Commits

Reviewing files that changed from the base of the PR and between c34b1a2 and a2c6343.

📒 Files selected for processing (5)

• .github/workflows/docker-image.yml
• Dockerfile
• Dockerfile.worker
• docs/deployment-architecture.md
• tests/container-ci-contract.test.ts

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[supabase]

This pull request has been ignored for the connected project sjrfecxgysukkwxsowpy because there are no changes detected in supabase directory. You can change this behaviour in Project Integrations Settings ↗︎.

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[github-actions]

CI triage

CI failed on this PR. Automated classification of the 2 failed job(s):

• Container images / build-and-verify — needs investigation: inspect the failing step and uploaded diagnostics; rerun only after classifying the cause.
• PR required — needs investigation: inspect the failing step and uploaded diagnostics; rerun only after classifying the cause.

Compared with main CI run #7908 (cancelled).

Classification is evidence routing, not permission to ignore a failure. Exact quarantined Playwright identities remain governed by the flake ledger.

[devin-ai-integration]

Devin Review found 1 potential issue.

View 1 additional finding in Devin Review.