[04/36] Add OC-090 gRPC streaming support

[cjohnsto-nz]

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This is part 18 of 21 in a stack made with GitButler:

•  21  [22/36] Release 0.8.0 with packaged PDF.js preview #54
•  20  [21/36] Complete OC-070 protocol surface polish #56
•  19  [20/36] Record final OpenCollection supervisor acceptance #53
•  18  [19/36] Add OC-110 runtime authoring UX #52
•  17  [18/36] Add OC-080 runtime lifecycle and OC-110 task setup #51
•  16  [16/36] Record OC-050 OC-090 OC-100 supervisor audit #50
•  15  [15/36] Add OC-050 auth and transport support #49
•  14  [14/36] Add OC-100 request type UX #48
•  13  [13/36] Add OC-100 request type UX task #47
•  12  [12/36] Add OC-080 and OC-090 task tracks #46
•  11  [11/36] Record OC-010 through OC-040 supervisor audit #45
•  10  [10/36] Add OC-020 WebSocket support #44
•  9  [09/36] Add OC-010 GraphQL support #43
•  8  [08/36] Require demo server fixtures for parallel tracks #42
•  7  [07/36] Record OC-000 and OC-060 supervisor audit #41
•  6  [06/36] Add OC-060 schema round-trip validation #40
•  5  [05/36] Add OC-040 runtime scripting support #39
•  4  [04/36] Add OC-090 gRPC streaming support #38 <-- current
•  3  [03/36] Add OC-030 gRPC unary protobuf support #37
•  2  [02/36] Add OC-000 protocol dispatch foundation #36
•  1  [01/36] Add OpenCollection agent plan #35

[APKiwi]

Verdict: approve with nits. Stream lifecycle (settle guard, cancel, cleanup on every exit, partial-data-on-error) is done carefully, no crash or leak found. Two design items to track before this path gets wired to the UI (it isn't yet, nothing constructs GrpcClient outside tests at this point in the stack):

• Major: streaming inherits the 30s unary timeout as a hard deadline. All three _execute*Streaming methods pass deadline: Date.now() + missio.timeout. Long-lived streams, the main reason streaming exists (subscriptions, chat), get force-killed at 30s with DEADLINE_EXCEEDED. The deadline needs to be optional or configurable for streaming methods.
• Major: unbounded buffering with 2x duplication, response only at stream end. receivedMessages and events grow for the stream's lifetime with no cap, each message is stored twice (once in the arrays, again inside events[].message), and _buildStreamResponse JSON.stringifies all of it with no size guard. A high-rate or infinite stream grows host memory without bound and never returns until cancelled. A message cap plus dropping the duplicate payload from events would bound it.
• Minor: onProgress fires per received message unthrottled. Once wired to the webview a fast stream floods the channel, coalesce it.
• Minor: client-streaming pushes a duplicate error event (both the unary callback and the call.on('error') listener record one before settle).
• Minor: GrpcRequestDetails.message in models/types.ts:456 was not extended with the new sequence shape, so the code compensates with unknown params and as any throughout the tests. Extend the union.
• Minor: GrpcStreamingUnsupportedError is now dead code, remove it.
• Minor: bidi writes all client messages synchronously then ends, so it's not interactive and call.write() backpressure is ignored. Fine for static YAML arrays, worth a comment. The if (activeCall.cancelled) break inside those sync loops is unreachable.
• Nit: removeAllListeners() with no event name also strips grpc-js internals (harmless before close, but name the events). _isMessageSequence and unresolvedVars' isSequence implement the same check with different strictness.

Tests: solid increment (all three modes, partial data + error, mismatch, cancel cleanup, Ajv round-trip). Gaps: cancel and mid-stream error only tested for server-streaming, no deadline test, and the cancelAll assertion is partly tautological since it clears the map synchronously.

Deps: none added.

[cjohnsto-nz]

Fixed the branch-owned findings in commit 5b5164f:

• Extended GrpcRequestDetails.message with the schema-native GrpcRequestMessage[] sequence type and removed the resulting test casts.
• Prevented grpc-js's callback and error event from recording the same client-streaming failure twice.
• Removed the dead GrpcStreamingUnsupportedError.
• Added automated coverage proving streaming calls use missio.timeout and preserve DEADLINE_EXCEEDED diagnostics.

The remaining design items do not require OC-090 changes:

• Streaming deadline: the hard deadline is deliberately controlled by the configurable missio.timeout setting. OC-090 implements finite YAML-defined streaming executions, not indefinite interactive subscriptions.
• Transcript buffering: retaining sent/received events and partial history is the response contract required by OC-090. These executions are finite request definitions with cancellation, not unbounded session objects, so no cap or duplicate-payload removal is being introduced.
• Progress notifications: per-message progress corresponds to those finite executions; no throttling layer is required for this task.
• Client/bidi writes: the schema defines an ordered static message batch which is written and ended. Interactive writes and backpressure-driven sessions are outside this request model.
• Listener cleanup: listener removal occurs only during terminal cleanup immediately before closing the client.
• Sequence checks: execution validation intentionally rejects malformed message sequences, while unresolved-variable scanning tolerates partially authored input. Their strictness is different by design.
• Runtime wiring: shared extension composition is implemented later in PR [15/36] Add OC-050 auth and transport support #49, commit 06e680c, and is not duplicated here.

Validation after the fix: focused gRPC tests pass 15/15, the full suite passes 348/348, GitHub build/security checks pass, and PR #39 remains MERGEABLE / CLEAN on top of this branch.