[snimu]

When you opened a session that had spawned subagents, we used to load every finished subagent back into memory as a full runtime, immediately, whether or not you ever looked at them. That's wasted memory and startup time.

With this change, finished subagents just stay on disk. They only get loaded when something actually touches them: you attach to one, read its transcript, send it a message, or delete it. Until then they're just a registry entry and a transcript file.

Details worth knowing:

• Lists (the agents view, list_subagents, etc.) show these on-disk children without loading them.
• If two things try to wake the same child at once, they share one load instead of racing each other.
• Deleting an on-disk child marks it deleted in the registry but keeps its files, same as deleting a live one.

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This is part 1–7 of a stack (each PR builds on the one before it):

1. feat(coding-agent): lazy child session hydration #583 — don't load finished subagents until someone needs them
2. feat(coding-agent): persist parent edges and derived depth for all sessions #584 — record each session's parent and depth on disk
3. feat(coding-agent): /rlm-max-depth session command #585 — new /rlm-max-depth command to control how deep agents can nest
4. feat(coding-agent): recursive scoped agents view #586 — browse the agent tree in the agents view
5. feat(coding-agent): delete child-agent inspector; one subagent summary line #587 — replace the child-agent inspector with one summary line
6. feat(coding-agent): whole-tree idle eviction #588 — shut down worker processes whose sessions have all gone idle
7. feat(coding-agent): intra-tree child session passivation #589 — quietly unload idle child sessions inside a running worker

Tests: the full suite at the top of the stack fails only on tests that already fail on the base branch. Each branch in the stack also passes checks and its own tests independently.

Note

Add lazy hydration of passive child sessions in the coding agent daemon

• Passive RLM subagents (completed children persisted to disk) are now enumerated from registry files without creating runtimes, and appear in list, attach, create, observe, and messaging commands.
• When a command targets a passive subagent, the daemon hydrates it on demand by walking the ancestor chain and restoring runtimes in order, deduplicating concurrent hydration via openingSessions.
• AgentSession.listRlmSubagents is now async and merges daemon-reported passive children into local results; deleteRlmSubagent handles passive entries with stricter ambiguity detection.
• Protocol schema is bumped to revision 9 (DAEMON_SCHEMA_REVISION) to advertise the new rlmDepth field on passive session rows.
• Risk: registry IO throughout the daemon is now async; callers that previously accessed listRlmSubagents synchronously must now await it.

Changes since #583 opened

• Added reservation checking to AgentDaemon.rehydrateCompletedRlmSubagent method to wait for concurrent explicit session opens [617ecca]
• Added test coverage for reservation-based hydration coordination behavior [617ecca]

^{Macroscope summarized 0e6a645.}

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Note

Medium Risk
Touches daemon session lifecycle, RLM registry IO, cron heartbeat restore, and async breaking changes to listRlmSubagents and host controllers; race coalescing is new but heavily tested.

Overview
Lazy passive RLM children replace eager rehydration of every completed subagent when a parent opens. The daemon walks persisted rlm-subagents.jsonl registries to list passive children (including nested trees and non-resident saved roots) without creating runtimes, and bumps daemon schema revision 9 with rlmDepth on passive session rows.

On-demand hydration runs when create, attach, agent messaging, agent_observe, or RLM heartbeat restore targets a passive child: the ancestor chain is rehydrated in order, concurrent opens share openingSessions, and half-bound sessions wait on bindingCompletions instead of failing as unavailable.

AgentSession makes listRlmSubagents async, merges daemon-reported passive children (via sessionDir on agent summaries), and extends deleteRlmSubagent for passive-only children (optional session on deleteRlmSubagentRuntime, ambiguity checks against async listAgents). Host handlers for agent message, observe, and RLM list now await controllers that may return promises.

Supervisor paths forward create to the owning worker when the target is a passive child row, and retain passive summaries in cross-worker agent peer sync.

^{Reviewed by Cursor Bugbot for commit 617ecca. Bugbot is set up for automated code reviews on this repo. Configure here.}

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