Skip hook loading and lifecycle events for subagents by dakotafabro · Pull Request #10596 · aaif-goose/goose

dakotafabro · 2026-07-20T23:48:45Z

Problem

When goose delegates a task to a subagent, the subagent creates a fresh Agent instance that loads the full hook lifecycle - discovering plugins, parsing hooks.json, compiling matchers, and firing SessionStart. This means every delegate triggers events meant for user-facing sessions: banner scripts execute mid-conversation, session-tracking plugins log phantom sessions, and any plugin subscribing to lifecycle events receives signals that violate the hook contract.

How this was discovered

While building goose-banner - a plugin that replaces the default "goose is ready" message with useful session context (active threads, token spend, project state) - the banner scripts were firing every time a delegate spun up. This surfaced the broader issue: the hook system's SessionStart event doesn't actually mean "a user started a session" - it fires for subagents too, which breaks the contract plugins rely on.

Benefit

Hook contract correctness. SessionStart fires exactly once per user-facing session. Subagents no longer trigger lifecycle events. Plugin authors can trust the signals they receive without building their own "am I a subagent?" guards.

Ecosystem scalability. As the plugin ecosystem grows (permission gates, audit logging, compliance checks, session tracking), every new plugin multiplies the per-delegate overhead today. After this fix, the cost of adding plugins stays zero for subagents permanently.

No more mid-session noise. Banner output, session counters, and state initialization no longer fire during delegates. The terminal stays clean. Plugins that track session state don't log phantom sessions.

Foundation for plugin trust. Plugins like goose-banner and spore (retrieval tracking, interoception) rely on SessionStart to initialize per-session state. Without this fix, subagent-triggered SessionStart overwrites the parent session's state mid-conversation.

Fix (two mechanisms)

1. Skip hooks for subagents

Adds is_subagent: bool to AgentConfig (defaults false). When true, Agent::with_config assigns an empty HookManager::default() instead of calling HookManager::load(). Both delegate paths in summon.rs (sync and async) set is_subagent = true.

2. Prevent double-emission in the parent

Adds an AtomicBool guard (session_start_emitted) to Agent. The CLI banner path sets it via emit_hook_with_banners, and reply() uses an atomic swap to skip if already fired. Non-CLI paths (gateway, ACP server, scheduler) that only go through reply() still emit exactly once via the same guard.

What this does NOT affect

Extension loading (MCP servers) - completely separate system, untouched. Each subagent still spins up its own independent MCP client processes.
Extension cleanup - subagent destruction relies on Rust's ownership/drop semantics. Fully intact.
SessionEnd hooks - were never fired for subagents even before this change.
Provider configuration - untouched
Session management - untouched
Parent session hooks - still fire normally

Performance (real but secondary)

Per-delegate overhead eliminated:

Operation	Before (per delegate)	After
Plugin filesystem scan	~2-5ms	0
hooks.json parse + regex compile	~1-2ms per plugin	0
SessionStart script execution	~50-200ms (process fork + I/O)	0
Hook matcher evaluation per tool call	~0.1ms per call per plugin	0

Savings are marginal today (~50s/week for a heavy user with 3 plugins), but compound as the plugin ecosystem grows.

Commits

feat: session banner hooks - adds emit_hook_with_banners to the CLI path so plugins can surface context at session startup (the feature that exposed the bug)
Skip hook loading for subagents - is_subagent flag on AgentConfig, empty HookManager for delegates
Prevent duplicate emission - AtomicBool guard ensures SessionStart fires at most once per Agent instance regardless of code path

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dakotafabro · 2026-07-21T00:06:42Z

🤖 Addressed - added an AtomicBool guard (session_start_emitted) to Agent. The CLI banner path sets it via emit_hook_with_banners, and reply() uses an atomic swap to skip if already fired. Non-CLI paths (gateway, ACP, scheduler) that only go through reply() still emit exactly once via the same guard. See 6e60aee.

SessionStart hooks can now return {"banner":"..."} on stdout to contribute lines to the CLI startup banner. Multiple plugins can each provide banner content, printed between 'goose is ready' and the context usage bar. This enables plugins like session-continuity tools, project dashboards, and reminder systems to surface information at the moment it's most useful - before the user types their first prompt. Backwards compatible: hooks that don't output JSON or lack a banner field behave exactly as before.

Subagents were creating a full HookManager on every delegate spawn, discovering all enabled plugins, parsing hooks.json files, compiling regex matchers, and then firing SessionStart (which executed user scripts like banner generators mid-session). This adds is_subagent to AgentConfig (defaults false) and assigns an empty HookManager when true, eliminating plugin discovery overhead and preventing spurious lifecycle events during delegation.

When the CLI calls emit_hook_with_banners(SessionStart) for banner collection, mark the event as already emitted so reply() does not fire it again on the first agent turn. Non-CLI paths (gateway, ACP server, scheduler) that go directly through reply() still emit it once via the atomic swap guard.

dakotafabro · 2026-08-07T22:07:37Z

🤖 Rebased onto current main. Conflict resolved (unused imports from earlier iteration removed). CI was green before, should pass again on the new base.

Ready for review whenever someone has bandwidth.

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chatgpt-codex-connector · 2026-08-07T22:09:55Z

+        if event == crate::hooks::HookEvent::SessionStart {
+            self.session_start_emitted.store(true, Ordering::Release);
+        }


Guard SessionStart in the state-machine path

When GOOSE_STATE_MACHINE=1 is enabled for a fresh interactive session, this flag only suppresses the legacy reply emission; StateMachine::emit_entry_hooks still emits SessionStart unconditionally at crates/goose/src/agents/state_machine/machine.rs:64-70. Consequently, the hook executed for the banner in session/mod.rs runs again when the first prompt enters the state machine, repeating setup, analytics, or other side effects. Fresh evidence beyond the earlier comment is that the legacy branch now checks this atomic at agent.rs:1936, while the state-machine branch does not, so the suppression needs to be shared with and tested in both paths.

AGENTS.md reference: AGENTS.md:L21-L23

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alexhancock · 2026-08-10T17:26:35Z

Thanks for the submission! It makes sense to me. Merging.

* origin/main: fix(mcp): prune dead notification subscribers (#11032) chore: remove the extension and tool count suggestion (#10869) feat: compaction in the GDK (#11042) fix(provider): retry transient errors on first stream item before ending turn (#10968) feat(cli): add /new to start a fresh session without restarting (#10767) feat(acp): title new sessions from _meta.sessionTitle (#10712) fix: adjust rmcp::model::Meta ref (#11107) Skip hook loading and lifecycle events for subagents (#10596) Sanitize Unicode tags in Responses output (#10745) fix(conversation): sanitize nested tool responses (#10609) fix(hints): bound recursive file expansion (#10546) fix(providers): drop stale signed thinking blocks after a mid-conversation model switch (#10007) fix(desktop): clarify compact cost display (#11093) Index messages by (session_id, created_timestamp, id) to stop on-disk sort storms (#10874) docs: add tool shim guide covering when to enable, backends, and troubleshooting (#10858) fix(deep-link): route extension/session deep links to regular windows not standalone app windows (#10908) fix(ui): raise chat input z-index so slash menu appears above loading indicator (#11015) fix(ui): support remote working directory for external backend (#10827)

* main: fix(mcp): prune dead notification subscribers (#11032) chore: remove the extension and tool count suggestion (#10869) feat: compaction in the GDK (#11042) fix(provider): retry transient errors on first stream item before ending turn (#10968) feat(cli): add /new to start a fresh session without restarting (#10767) feat(acp): title new sessions from _meta.sessionTitle (#10712) fix: adjust rmcp::model::Meta ref (#11107) Skip hook loading and lifecycle events for subagents (#10596) Sanitize Unicode tags in Responses output (#10745) fix(conversation): sanitize nested tool responses (#10609) fix(hints): bound recursive file expansion (#10546) fix(providers): drop stale signed thinking blocks after a mid-conversation model switch (#10007) fix(desktop): clarify compact cost display (#11093) Index messages by (session_id, created_timestamp, id) to stop on-disk sort storms (#10874) docs: add tool shim guide covering when to enable, backends, and troubleshooting (#10858) fix(deep-link): route extension/session deep links to regular windows not standalone app windows (#10908) fix(ui): raise chat input z-index so slash menu appears above loading indicator (#11015) fix(ui): support remote working directory for external backend (#10827)

dakotafabro marked this pull request as ready for review July 20, 2026 23:50

chatgpt-codex-connector Bot reviewed Jul 20, 2026

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Comment thread crates/goose-cli/src/session/mod.rs

alexhancock self-assigned this Jul 30, 2026

dakotafabro added 3 commits August 7, 2026 14:58

dakotafabro force-pushed the fix/skip-hooks-for-subagents branch from 6e60aee to 7781486 Compare August 7, 2026 22:07

chatgpt-codex-connector Bot reviewed Aug 7, 2026

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alexhancock self-requested a review August 10, 2026 17:25

alexhancock approved these changes Aug 10, 2026

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alexhancock merged commit 3e15ccb into aaif-goose:main Aug 10, 2026
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aeoess mentioned this pull request Aug 10, 2026

feat(hooks): add PreToolUseResult event and stable tool_call_id across tool lifecycle #11120

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dakotafabro mentioned this pull request Aug 11, 2026

feat: session banner hooks - let plugins surface context at startup #10562

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github-actions Bot mentioned this pull request Aug 11, 2026

chore(release): release version 1.46.0 #11151

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Skip hook loading and lifecycle events for subagents - #10596

Skip hook loading and lifecycle events for subagents#10596
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Problem

How this was discovered

Benefit

Fix (two mechanisms)

1. Skip hooks for subagents

2. Prevent double-emission in the parent

What this does NOT affect

Performance (real but secondary)

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dakotafabro commented Jul 20, 2026 •

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