contrib: negative cache, upgrade compatibility, tx rejection explainer, relayer fallback

[ebubechi-ihediwa]

Summary

Four self-contained mock route suites under contrib/routes/, each addressing one assigned issue:

• [easy] Add negative caching for unknown contract hash lookups #285 – contrib/routes/issue-285-negative-cache-lookup-suite/: mock contract-hash lookup service with negative caching (30s TTL) for unknown-hash results, a metrics endpoint reporting negative cache hit rate, and the TTL rationale documented in the suite's README.
• [hard] Create a route suite simulating contract upgrade compatibility checks #107 – contrib/routes/upgrade-compatibility-suite/: current-version and check-upgrade endpoints comparing a proposed wasm hash's metadata (storage schema version, function signatures) against the currently deployed one, with a sample dataset containing one compatible and one incompatible upgrade pair.
• A11 - Safety policies: simulation and explanation of why a transaction would be rejected #23 – contrib/routes/issue-23-tx-rejection-explainer-suite/: evaluates a proposed transaction's authorization contexts against the same rules as contrib/contracts/safety-policy, naming the specific rule responsible for a rejection (max-transfer-amount, non-transfer-call, unknown-interaction, no-interactions) instead of a generic failure, and honestly reporting unknown when an interaction can't be classified rather than implying safety. The README documents how divergence from the on-chain contract is prevented.
• [medium] Create a mock route module simulating a relayer submission fallback path #80 – contrib/routes/relayer-fallback/: mock relayer submission route that falls back to a secondary path when the primary fails (forceable via a request flag for testing), reporting which path handled the submission.

Each suite is fully self-contained (its own route.mjs/.test.mjs/README.md), touches nothing outside contrib/, and has no dependency on the pnpm workspace or turbo pipeline.

Test plan

Ran each suite's test script directly (all pass) and checked formatting with the pinned Prettier config:

• node contrib/routes/issue-285-negative-cache-lookup-suite/route.test.mjs
• node contrib/routes/upgrade-compatibility-suite/route.test.mjs
• node contrib/routes/issue-23-tx-rejection-explainer-suite/route.test.mjs
• node contrib/routes/relayer-fallback/route.test.mjs
• prettier --check on all new files

Closes #285
Closes #107
Closes #23
Closes #80

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[ebubechi-ihediwa]

Closing to reopen from a renamed branch (contrib/mock-route-suites).