perf(terminal): defer MessagePort ACK to xterm write callback#4862
Merged
gregpriday merged 4 commits intodevelopfrom Apr 2, 2026
Merged
perf(terminal): defer MessagePort ACK to xterm write callback#4862gregpriday merged 4 commits intodevelopfrom
gregpriday merged 4 commits intodevelopfrom
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- Split ACK in installPortDataHandler: defer when live callbacks exist, immediate for early-buffered data (no xterm involved yet) - Add acknowledgePortData() method routing ACK via active MessagePort - Call acknowledgePortData in writeToTerminal for all three paths: hibernated, deferred-restore, and normal xterm write callback - Update tests: verify no immediate ACK on live-callback path, immediate ACK preserved for early-buffer, deferred ACK works
- Add pendingPortAckBytes FIFO queue preserving msg.bytes from pty-host - acknowledgePortData pops from queue to avoid UTF-16 vs UTF-8 mismatch - Skip port ACK when queue is empty (IPC data or early-buffer flush), preventing double-ACK for early-buffered data - Add tests for byte count preservation and empty-queue no-op behavior
…ce tests - Add acknowledgePortData: vi.fn() to terminalClient mock in 9 test files that mock the terminalClient module
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Summary
terminal.write()callback, matching the IPC path's behaviour and making the watermark system the actual flow control gate as intended.Resolves #4849
Changes
src/clients/terminalClient.ts: removed immediate ACK in the MessagePortmessageevent handler; callbacks now receiveidandbyteCountso callers can defer ACK to after xterm consumptionsrc/services/terminal/TerminalInstanceService.ts: passesidandbyteCountthrough to the existingterminal.write()callback alongside the IPC path's ACK callsrc/clients/__tests__/terminalClient.test.ts: updated and extended tests covering deferred ACK behaviour, byte count passthrough, and the multi-callback fan-outTesting
Unit tests updated and passing. The change aligns MessagePort backpressure semantics with the existing IPC path, which has been stable in production.