FM-PS-LYNX-014 T1+T4: adapters own Response; name NDJSON Accept policy

[djwok]

Implements T1 + T4 only from issue #34 on current main. Does not include T2 / ADR-0004 / LynxFetchModule streaming-fallback deletion, T3/NativeSql, or N1–N4.

T1 — Transport adapters own their Response

Each SyncStreamTransport interprets its own wire shape and returns a finished Response:

• NativeHttpFetch maps NativeHttpFetchEnvelope (streamingId vs idle-complete body / bodyBase64)
• LynxFetchModule maps LynxFetchSuccessPayload including lynxExtension.streamingId
• HostFetch keeps the identifier Fetch body and does not inspect Response.lynxExtension.streamingId

One internal constructor: syncStreamResponse({ bytes } | { streamingId } | { streamingFallback: true }). The fallback variant is the existing nameless GlobalEventEmitter path (left for the stacked T2 agent).

enterEarlyCapture() is removed from LynxRemote. Only NativeHttpFetch owns early capture (preserves #36 abort / retirement / multi-emitter / overflow).

response.ts exports shrink to three functions:

1. syncStreamResponse
2. stabilizeStreamingResponse
3. stabilizeJsonResponse

Plus the constructor init type SyncStreamResponseInit. Dropped from oxlint.config.ts ignore: bytes.ts, events.ts, response.ts.

T4 — Name NDJSON header policy

headerMap is a copy-only shape conversion. preferNdjsonAccept (BSON Accept → NDJSON, default Accept-Encoding: identity) runs at syncStreamRequestFromFetch. Behavior is unchanged for /sync/stream requests.

Tests

• Adapter ownership: NativeHttpFetch / LynxFetchModule return a finished Response from their own wire types
• HostFetch does not sniff lynxExtension.streamingId (getter trap + ignored custom stream name)
• headerMap does not rewrite Accept; the named seam does
• Existing fix(sync): abort native streams, drop iOS 150s cap, release earlyEvents #36 lifecycle and FM-PS-LYNX-012: hasSynced UX, waitForFirstSync, streaming README leftovers (#19 #20 #21) #40 UX tests kept

Verification

• pnpm typecheck — pass
• pnpm lint — pass
• pnpm test — 112/112 pass
• make test — native SQL RPC + shared NDJSON fixture checks pass

Paste-ready comment for #34

GitHub issue write access was not available from this agent (gh issue view 34 / issue list both 403). Suggested comment:

T1 + T4 implemented on current main: #44

T1: Each SyncStreamTransport returns a finished Response and owns its wire shape. syncStreamResponse({bytes}|{streamingId}|{streamingFallback}) is the one constructor. enterEarlyCapture lives only on NativeHttpFetch. HostFetch no longer reads lynxExtension.streamingId. response.ts exports are syncStreamResponse, stabilizeStreamingResponse, stabilizeJsonResponse. Transport files dropped from the oxlint ignore list.

T4: preferNdjsonAccept is applied in syncStreamRequestFromFetch; headerMap only copies.

Not in this PR: T2 / ADR-0004 / LynxFetchModule streaming-fallback deletion, T3/NativeSql, N1–N4.

#36 stream lifecycle (abort, retirement, multi-emitter, overflow) and #40 UX are preserved. pnpm typecheck, pnpm lint, pnpm test (112), and make test all pass.