Summary

The user-facing /abort command and the gateway sessions.reset / sessions.delete methods lost their subprocess-termination semantics in the pi-embedded gut (b27cecc795, #76/#77). Both call sites were rewiring points for ChannelBridge; replacements (killSessionRun + waitForSessionRunEnd) exist in src/agents/session-run-registry.ts but were never wired to them — they left behind three const aborted = false; / const ended = true; dead placeholders.

This PR wires the three call sites. Same family as #2460 (gateway capacity accounting) and #2461 (subagent kill/steer), completing the trio of session-run-registry integrations that were outstanding after the gut.

Changes

Plus one import per file and a new SESSION_RUN_TERMINATION_TIMEOUT_MS = 15_000 constant grouped with the sibling ACP_RUNTIME_CLEANUP_TIMEOUT_MS.

Note on stale AC3

Issue #2343 lists three regression sites. The third (commands-session.ts::applyAbortTarget) does not exist in the current tree — git grep applyAbortTarget returns zero hits. The /session abort pathway was consolidated into abort.ts::tryFastAbortFromMessage at some earlier point, so no duplicate wiring is needed. AC3 marked N/A.

Behavior change (intended, per AC)

sessions.reset / sessions.delete:

• Before: returned success instantly regardless of active subprocess (const ended = true; placeholder).
• After: wait up to 15s for the CLI subprocess to terminate. On success → returns undefined (success). On timeout → UNAVAILABLE error with the pre-gut message "Session ${params.key} is still active; try again in a moment.".

/abort command (non-ACP sessions):

• Before: marked abortedLastRun = true and cleared queues, but the CLI subprocess kept running until natural completion.
• After: dispatches abortController.abort() or process.kill(pid, "SIGTERM") via killSessionRun; the aborted field in the return value now reflects reality.

Key-format alignment

killSessionRun keys on canonical sessionKey. All three call sites already operate in canonical space:

• abort.ts subagent loop: childKey from parseAgentSessionKey (canonical)
• abort.ts fast-abort: resolvedTargetKey = key ?? targetKey from resolveSessionEntryForKey (canonical)
• sessions.ts: params.target.canonicalKey (canonical by construction via resolveGatewaySessionStoreTarget)

No conversion risk. Inherits the registration-vs-kill key discipline established in PRs #2460 / #2461.

Verification

• pnpm check (format + tsgo + lint + project-specific lints) → exit 0
• pnpm test (full parallel suite) → 800 files / 7010 passed / 3 skipped — no regression
• Rescans:
  • git grep "const aborted = false" → zero hits (combined sweep of fix(subagents): wire kill and steer actions to session-run-registry killSessionRun #2344 + this PR)
  • git grep "abortEmbeddedPiRun" → only test-mock contexts; production has no remaining references
• Adversarial validation (fresh-context subclaude, 7 AC + 9 adversarial checks): CLEAN. Confirmations:
  • waitForSessionRunEnd is LIVE (50ms poll tick, max 15s wall-clock, non-blocking async)
  • ensureSessionRuntimeCleanup callers always pass a valid canonicalKey
  • No user-facing surface depends on the old always-false aborted field (callers read .handled and .stoppedSubagents only)
  • killSessionRun never throws (internal try/catch around process.kill)
  • Zero new @ts-expect-error / @ts-ignore / as any introduced

Test plan

• pnpm check exit 0
• pnpm test full suite green (7010 / 800 files)
• Rescans clean
• CI green on all required checks

Context

• Parent: audit: review all Pi engine stub replacements for ChannelBridge compatibility #2089 (ChannelBridge compatibility audit)
• Sibling PRs (already merged): fix(gateway): count active CLI runs in restart deferral — prevents mid-turn termination #2460 (gateway capacity via getActiveSessionRunCount) + fix(subagents): wire kill and steer to killSessionRun — actually terminate CLI subprocesses #2461 (subagents via killSessionRun)
• Regression introduced by: Remove pi-embedded.ts stub barrel and clean up no-op call sites #76/feat: remove pi-embedded.ts stub barrel and clean up call sites (#76) #77 (pi-embedded gut, b27cecc795)
• Replacement module: src/agents/session-run-registry.ts

Closes #2343

Refs: #2089, #2344, #2460, #2461

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