feat(indexer): add ETag caching for GET /streams and GET /splits responses

[olatechy0]

Summary

Closes #674 — Return an ETag header on GET /streams and GET /splits responses based on the last-updated timestamp of the data, and respond with 304 Not Modified when the client sends a matching If-None-Match header.

Changes

indexer/src/server.ts

• Added computeEtag — a strong ETag derived from a SHA-256 hash of the canonical JSON body joined with the data's last-updated timestamp. It is stable across identical payloads and changes the instant the underlying data changes.
• Added jsonWithEtag — writes the ETag header on every 200 response and answers 304 Not Modified (no body) when If-None-Match matches the current ETag.
• Wired If-None-Match into handleStreams.
• Added the missing GET /splits indexer endpoint (the SDK already calls {indexerUrl}/splits but the route did not exist), serving the account's current splits config with the same ETag/304 behavior.

indexer/src/db.ts

• getDripsStreamsLastUpdated(account) — most recent created_at/ended_at across an account's streams, for the /streams ETag.
• getDripsSplitsLastUpdated(account) — most recent updated_at across an account's current_streams rows, for the /splits ETag.
• queryDripsSplits(account) — aggregates the account's splits receivers from current_streams (verbatim stream_set receivers) with a stable SHA-256 hash and a last_updated value.

Behavior

• GET /streams?account=…&network=… → 200 with ETag; 304 (no body) when If-None-Match matches; a new ETag as soon as stream data changes.
• GET /splits?account=…&network=… → 200 with ETag; 304 when If-None-Match matches; a new ETag when the account's splits config changes.
• Error responses (400/404/405/500) are unchanged.

Tests (indexer/test/drips-api.test.ts)

Added focused regression tests for both endpoints covering the acceptance criteria:

• First request returns 200 with an ETag header.
• Unchanged data + matching If-None-Match returns 304 with no body.
• Changed data returns a different ETag (stream added; splits config updated), and the new ETag then validates to 304.

Verification

• npx ts-node --transpile-only test/drips-api.test.ts → passes (covers the ETag scenarios).
• npx ts-node --transpile-only test/drips-events-projection.test.ts → passes.
• npx tsc --noEmit in indexer/ shows only two pre-existing errors in the gives handler (GiveQueryParams/queryGives not defined at HEAD); db.ts has no errors. The root tsconfig.json excludes indexer, so CI's backend-build type-check does not cover the indexer.
• The root vitest run suite has pre-existing failures at HEAD (tough-cookie/jsdom module resolution, and gives-endpoint tests that depend on the undefined queryGives) — identical failure set on main; this change adds no new failures.

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[libby-coder]

RESOLVE CONFLIUCTS

[olatechy0]

@libby-coder @Ceejaytech25 - The branch conflicts are resolved and the branch is up to date with main.

I merged the latest main into feat/etag-caching and resolved the conflicts in indexer/src/db.ts and indexer/src/server.ts, keeping the ETag/304 additions intact alongside main's surrounding reformatting.

Verification:

• npx tsc --noEmit in indexer/ passes
• npm run test:drips-api passes (covers the ETag / 304 / changed-data scenarios)

The PR is now conflict-free and mergeable - ready for review. CI is just waiting on approval to run for this fork PR.

Thanks!