Summary

• add stdout/stderr error handlers to Matrix dependency bootstrap commands
• align the stream-error path with the established src/node-host/invoke.ts lifecycle pattern: record the first stream error, send one SIGTERM, keep the process-exit cleanup registered, escalate to SIGKILL if the child does not exit, and settle only from the child close event
• remove the production spawn override that an earlier revision of this branch added for testing; the runtime command path is fixed and takes no injection seam
• cover the stream-error lifecycle with a real spawned node child over real stdio pipes in a focused regression test
• collision check: no open PR found for the Matrix dependency command stream-error issue or extensions/matrix/src/matrix/deps.ts; the only fuzzy search hit was an unrelated Telegram PR

Verification

• node scripts/run-vitest.mjs extensions/matrix/src/matrix/deps.test.ts — passed; 1 file, 10 tests passed
• ./node_modules/.bin/oxfmt --check --threads=1 extensions/matrix/src/matrix/deps.ts extensions/matrix/src/matrix/deps.test.ts — all files correctly formatted
• ./node_modules/.bin/oxlint --tsconfig config/tsconfig/oxlint.extensions.json extensions/matrix/src/matrix/deps.ts extensions/matrix/src/matrix/deps.test.ts — no findings
• mutation check: changing the stream-error guard to allow duplicate stream errors made the focused test fail with expected "kill" to be called 1 times, but got 2 times; restoring the guard made the same test pass

Real behavior proof

Behavior addressed: Matrix dependency command stdout/stderr stream errors no longer settle the command result before child close, no longer remove the process-exit cleanup early, and duplicate stream errors cannot trigger teardown twice.
Real environment tested: local Linux Node 22.22 source checkout; the regression test drives the real exported runFixedCommandWithTimeout helper with a real spawned node child process and real pipe-backed stdout/stderr.
Exact steps or command run after this patch: the test destroys the parent-side stdout/stderr Readable with an error while the real child is alive, then observes SIGTERM, SIGKILL escalation, and settlement from the child close event; command: node scripts/run-vitest.mjs extensions/matrix/src/matrix/deps.test.ts.
Evidence after fix: the real-child regression asserts no settlement before close, exactly one SIGTERM for duplicate stream errors, retained process-exit listener during shutdown, SIGKILL escalation, child close { code: null, signal: "SIGKILL" }, and exit-listener cleanup after settlement.
Observed result after fix: Test Files 1 passed (1); Tests 10 passed (10).
What was not tested: a live Matrix bootstrap download. The test injects the Readable error on the parent side because a real download-lib.js child cannot deterministically produce a parent read-side error: normal child exit, fd close, and SIGKILL surface as EOF/close on the parent read side, and EPIPE is a write-side failure.