Complete APT provider design and implementation review

[omry]

Objective

Perform a complete, coordinated design review of:

• docs/APT_PROVIDER.md
• docs/APT_PROVIDER_DETAIL_DESIGN.md

The APT provider is already fully implemented. Treat the implementation and
tests as the evidence surface: determine whether both design documents describe
the shipped behavior accurately, whether the implementation satisfies their
normative contracts, and whether the two documents agree with each other and
with docs/BLUEPRINT_ENVIRONMENT_MODEL.md at their stated authority boundaries.

Review scope

• Review the conceptual product semantics in APT_PROVIDER.md.
• Review the concrete Go types, package boundaries, state, Docker operations,
  migrations, failure handling, and implementation gates in
  APT_PROVIDER_DETAIL_DESIGN.md.
• Trace every normative behavioral, security, identity, lifecycle, persistence,
  concurrency, and failure-semantics claim to the implementation and tests.
• Review the implementation in the opposite direction for material behavior,
  constraints, defaults, or trust assumptions absent from the documents.
• Reconcile disagreements between the conceptual design, detailed design,
  Blueprint Environment Model, implementation, and tests according to their
  declared authority rather than silently harmonizing prose.

Review requirements

• Run the complete deep-design-review workflow over both documents as one
  coordinated review, with separate per-document evidence where useful.
• Verify every implementation claim against code before accepting a finding or
  changing a document. Search misses are not evidence that behavior is absent;
  use case-insensitive searches, symbol tracing, call-chain inspection, and
  alternate package/file names before classifying anything as unimplemented.
• Classify findings clearly, including conflicting, unimplemented, additive,
  stale, or ambiguous behavior.
• Distinguish truth fixes from representation fixes. Do not make a stale design
  internally consistent and call the underlying implementation mismatch fixed.
• Record implementation gaps in docs/BACKLOG.md when they are intentionally
  deferred, with links back to the durable review decision.

Deliverables

• A dispositioned finding register with code and document evidence.
• Reconciled design text for every accepted documentation finding.
• Durable review sidecars under docs/.review/ for both documents, including
  reviewed-byte attestations and standing decisions.
• Reconstructible working review trails under temp/reviews/.
• Backlog entries for every accepted implementation gap that is not fixed in
  the review change.
• A final clean review verdict only after every finding is verified, rejected,
  or explicitly deferred.

Completion criteria

• Both APT design documents have received complete review coverage.
• Their authority boundary and shared contracts are mutually consistent.
• Every material design claim has code evidence, and every material shipped
  behavior has an explicit design owner.
• No unresolved finding is hidden by wording changes or left only in temporary
  review state.