Checkpoint web parity through Chromium input tasks

docs/status/M13-04G.md

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+# M13-04G Status
+
+status: done  
+task: server process-tree cancellation  
+updated: 2026-08-19 America/New_York  
+enablingTask: false  
+parityStateChange: false
+
+## Scope
+
+Real server jobs now run in a detached process group on POSIX and are cancelled as a tree. The cancellation
+path sends SIGTERM to the group, escalates to SIGKILL after the grace window, waits for the group to exit,
+and performs one idempotent job-directory cleanup. Windows uses `taskkill /T /F`. The receipt reports the
+actual signal path, cleanup count and orphan count. Execution remains `DISABLED`.
+
+## Evidence
+
+- `npm --prefix web run test:server-job-cancellation` passed 2/2 real-process unit tests and the checker.
+- Checker output: `server-job-cancel-ok state=CANCELLED tree=SIGTERM_GROUP cleanup=1 orphan=0 residual=0 execution=DISABLED next=M13-04H`.
+- `git diff --check` passed.
+
+## Artifact Hashes
+
+- parent manifest: `b5b4b26183dc48ebcae009e49999010d9b60d512f5daa4674a0aff0577d6602c`
+- protocol: `74fbbac806f34904bc9cb8e40eaf386cb60d44d978973950f1809262d311ec95`
+- checker: `751ecafc642595d0de69b618e223cbff49d414f2958fc371371e4a668d66a8cc`
+- unit: `39ac445ff51a9bfe249363204cf2edca906b16bf67ab1f8321166b440eba8629`
+- package: `ca092a9a1d48ac41dc20f978bb26c8268adde9f7602a06459c7df8c2cb2d4cc7`
+- report: `61f5c3ad315f94bac48e58627fcc46015c173dd9f303d5914acb8dbbe93caa97`
+
+## Next Task
+
+`M13-04H`: map timeout/OOM/non-zero exit/signal to stable error codes.
+
+## Rollback
+
+Remove the process control protocol, unit/checker, report, manifest, package command and this status entry;
+restore `M13-04F` as the queue tail.