Cross-Platform Contract Propagation Audit

Overview

Audit a contract change from its source through every transformation and consumer before release. Treat a field that exists in one schema as incomplete until its meaning, defaults, wire behavior, rollout controls, client handling, analytics, and tests are proven across all relevant paths.

This is a read-only evidence workflow. It reports propagation gaps; it does not implement them.

When to Use This Skill

• Use when adding or changing a field, enum value, status, capability, or feature flag shared by multiple components.
• Use when database, backend, API, Web, Android, iOS, jobs, events, or analytics may interpret the same value differently.
• Use when a change must preserve existing records, older clients, or a default-off rollout.
• Use when a change looks complete in one endpoint but may be missing from alternate entry points or generated models.

How It Works

Step 1: Write the semantic contract

Before tracing files, state the business invariant and define every observable state. Distinguish values that languages and serializers often collapse:

State	Questions to answer
missing	Is the property absent on the wire or in an old record?
null	Is it unknown, inherited, unsupported, or invalid?
false or zero	Is this an explicit disabled value or a default?
true or non-zero	What behavior becomes available?
unknown enum	Must old consumers ignore, preserve, or reject it?

Record compatibility requirements, ownership, rollout condition, and the exact user-visible or system behavior for each state. Do not accept optional, nullable, and default false as equivalent without evidence.

Step 2: Enumerate the propagation graph

List every relevant node before judging completeness:

source of truth
  -> persistence and migration
  -> domain model and mapper
  -> service or policy computation
  -> every API, event, cache, and job projection
  -> generated or handwritten client model
  -> client state and presentation logic
  -> analytics and operational observability
  -> tests, rollout, and rollback checks

Include alternate read/write endpoints, list/detail projections, background consumers, offline caches, admin surfaces, older app versions, and feature-flag evaluation points when they are in scope. Mark a node not applicable only with a reason.

Step 3: Trace evidence edge by edge

For each edge, cite the producer, transformation, consumer, and test using file paths, symbols, schema names, or other inspectable evidence. Assign one status:

Status	Meaning
proven	Producer and consumer agree, with direct evidence and relevant test coverage.
partial	Some paths or states agree, but coverage is incomplete.
missing	A required propagation edge or consumer is absent.
conflict	Two layers implement different semantics.
unknown	Evidence is unavailable or ambiguous.
not_applicable	The layer is outside scope, with a stated reason.

Do not upgrade likely, convention, type compatibility, or a framework default to proven. A declaration proves shape, not runtime mapping or behavior.

Step 4: Check the high-risk boundaries

Inspect these boundaries explicitly:

• Migration and existing data: default, backfill, nullability, rollback, mixed-version reads and writes.
• Domain mapping: missing/null coercion, enum fallbacks, validation, derived values, serialization symmetry.
• Fan-out surfaces: list and detail DTOs, events, caches, jobs, search indexes, SDKs, and alternate API versions.
• Client compatibility: missing and explicit-null decoding, unknown enums, generated-model drift, cached payloads, release or minified builds.
• Rollout control: flag default, evaluation location, cohort consistency, kill switch, and behavior when stored data disagrees with the flag.
• Analytics: offered, rendered, attempted, succeeded, and failed events carry enough contract and version context to join reliably.

Step 5: Build a state-by-path test matrix

Cross the semantic states from Step 1 with every material path from Step 2. At minimum, include existing-data defaults, enabled and disabled values, flag on and off, alternate endpoints, current clients, and representative older clients.

For each cell, record the expected result, evidence, and status. A unit test at one layer does not prove an end-to-end cell. Use unknown for unexecuted cells.

Step 6: Decide against explicit release gates

Derive gates from the stated contract, not from intuition. A release is blocked when an edge or compatibility invariant that the contract explicitly requires is missing, conflict, or unknown, or when rollback cannot contain the new behavior. Use inconclusive only when the release contract itself is absent or ambiguous, so the audit cannot determine which edges or invariants are required. Do not downgrade a known required but unproven gate from blocked to inconclusive.

Return the smallest verification or repair set that would change the verdict. Keep implementation suggestions separate from proven findings.

Example

For a nullable can_complete field that should expose an action only when both the stored capability and server flag are true:

Invariant: show action = (feature_flag == on) AND (can_complete == true)

Path                                      Status    Evidence
DB null -> domain false -> detail API     partial   mapper exists; null case untested
DB true + flag off -> detail API          unknown   flag branch not tested
DB true + flag on -> list API             missing   list DTO omits field
missing field -> Web hidden               proven    client test covers missing
explicit null -> Android hidden           unknown   decoder behavior untested
impression -> click attribution           missing   click event lacks capability/cohort

Verdict: blocked by the missing list projection and incomplete flag enforcement;
older-client and explicit-null compatibility remain unverified.

Best Practices

• Start from behavior and state semantics, then trace code; do not start from a filename guess.
• Search for field names, serialized aliases, enum values, DTOs, mappers, flags, and analytics events.
• Cite negative searches with their scope and revision; absence claims require a bounded search.
• Separate source-of-truth behavior from client presentation and telemetry.
• Verify all entry points that can produce the same user-visible state.
• Keep findings reproducible: contract, revision, evidence, status, impact, and next check.

Limitations

• Static evidence cannot prove runtime configuration, deployed schema state, generated-code freshness, or client behavior that was not exercised.
• Repository access may omit private services, analytics schemas, remote flags, or older released clients; mark those edges unknown.
• This skill finds propagation and semantic gaps, not every security, performance, or product-design defect.
• A complete graph does not prove the underlying business rule is correct.

Security & Safety Notes

• Keep the audit read-only unless the user separately authorizes implementation or runtime testing.
• Redact production records, credentials, user identifiers, and sensitive payload fields from evidence.
• Do not enable flags, mutate data, publish schemas, or exercise production actions merely to fill an evidence gap.

Common Pitfalls

• Problem: The field exists in the database and one response, so the change is called complete. Solution: Trace every projection and consumer, including alternate endpoints and events.
• Problem: Missing, null, and false are treated as the same state. Solution: Define and test each state at every serialization boundary.
• Problem: Type declarations are treated as runtime proof. Solution: Require mapping, decoding, behavior, and test evidence before using proven.
• Problem: The feature flag hides UI but not data or alternate APIs. Solution: Map every flag evaluation point and test stored-value/flag combinations.
• Problem: A green unit test suite is presented as cross-platform coverage. Solution: Build the state-by-path matrix and preserve unexecuted cells as unknown.

Related Skills

• @api-analyzer - Validate the correctness of an individual API request.
• @spec-to-code-compliance - Compare formal blockchain specifications with implementations.
• @technical-change-tracker - Record implementation progress and handoff state across sessions.