fix(historian): defer child session cleanup

[coleleavitt]

Summary

• stop deleting successful historian children on the prompt-return path
• retire stale historian children through the existing age-gated orphan sweep, including dreamer-disabled installs
• budget the stale threshold for outer retries, model-suggestion retry, and configured fallback models
• preserve historian children when keep_subagents is enabled
• raise the default historian prompt timeout from 5 to 10 minutes
• surface current OpenCode native Task wrappers whose completed <task_result> is empty

Closes #336.
Defensively addresses the silent empty-result symptom in #270.

Root cause

OpenCode prompt completion and session.idle are not global session-writer barriers. Detached step/summary writes can persist after either event. Immediate session.delete therefore races foreign-key-backed part inserts.

Verification

• red: successful historian lifecycle observed immediate deletion without a quiescence barrier
• green: 105 affected tests, 0 failures
• plugin build and declaration emit pass
• plugin typecheck passes
• Biome format check passes
• Oracle race review: SHIP

Notes

The sweep retains a minimum safety factor of 3 after accounting for all configured prompt candidates and retry layers. Recent/live children are not eligible.

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Summary by cubic

Defers historian child-session cleanup to an age-gated orphan sweep to avoid racing OpenCode’s detached writes and FK insert failures. Separates historian vs. privacy sweeps so privacy windows stay short while historian cleanup uses its own retry/fallback budget. Also raises the historian timeout and surfaces empty native Task completions for debugging.

• Keeps historian children after prompt completion; the orphan sweep removes them after a window that covers outer retries, model-suggestion attempts, and the normalized fallback chain. Excludes historian children from the sweep when keep_subagents is true.
• Preserves privacy windows: sweeps dreamer/privacy titles and historian titles separately. Privacy stale = task timeout × 3; historian stale = historian_timeout_ms × MAX_HISTORIAN_PROMPT_ATTEMPTS × (primary+suggested) × fallback_count.
• Runs the orphan sweep even when Dreamer is disabled. Registers historian timeout and normalized fallback count (via resolveFallbackChain) and derives privacy timeouts before scheduling.
• Updates configuration, docs, and schema: default historian_timeout_ms is 600000; exports MAX_HISTORIAN_PROMPT_ATTEMPTS = 3.
• Diagnostics: annotates completed native Task outputs with an empty <task_result> using a sentinel via the tool-execute-after hook.
• Migration: if you relied on the old 5-minute default, set historian_timeout_ms to 300000. Expect historian child sessions to persist until their sweep; privacy-only children retain their shorter sweep window.

Closes #336. Defensively addresses the empty-result symptom in #270.

^{Written for commit 61ec04c. Summary will update on new commits.}

Greptile Summary

This PR defers historian child-session deletion to an age-gated maintenance sweep, preventing deletion from racing detached OpenCode writes.

• Separates historian and Dreamer privacy sweeps so each uses its own runtime-derived stale window.
• Runs historian cleanup when Dreamer is disabled while honoring keep_subagents.
• Raises the default historian timeout to ten minutes and synchronizes the public configuration surfaces.
• Annotates completed native Task wrappers whose <task_result> is empty.

Confidence Score: 5/5

The PR appears safe to merge.

No blocking failure remains.

Important Files Changed

Filename	Overview
packages/plugin/src/hooks/magic-context/compartment-runner-historian.ts	Removes immediate successful-child deletion and retains historian sessions for deferred cleanup.
packages/plugin/src/features/magic-context/dreamer/retrospective-orphan-sweep.ts	Adds historian title matching and a stale threshold covering retries, suggestion attempts, and fallback models.
packages/plugin/src/plugin/dream-timer.ts	Runs separate Dreamer and historian orphan sweeps, including historian-only maintenance configurations.
packages/plugin/src/hooks/magic-context/empty-task-output.ts	Annotates completed native Task wrappers when their task-result body contains no final text.
packages/plugin/src/config/schema/magic-context.ts	Raises the historian timeout default and centralizes the maximum prompt-attempt count.
packages/plugin/src/index.ts	Supplies normalized historian timeout, fallback count, and retention settings to timer registration.

Sequence Diagram

sequenceDiagram
    participant H as Historian runner
    participant O as OpenCode session
    participant W as Detached writers
    participant T as Maintenance timer
    participant D as OpenCode DB
    H->>O: Create and prompt child session
    O-->>H: Prompt completes
    H-->>O: Preserve child session
    W->>D: Persist remaining step/summary parts
    T->>D: Find historian children older than stale threshold
    T->>O: Delete stale child unless keep_subagents

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_{Reviews (3): Last reviewed commit: "fix(historian): preserve child privacy w..." | Re-trigger Greptile}

Context used:

• Knowledge Base — Magic Context plugin runtime
• Knowledge Base — Configuration and public contracts

[cubic-dev-ai]

1 issue found across 15 files

Prompt for AI agents (unresolved issues)

Check if these issues are valid — if so, understand the root cause of each and fix them. If appropriate, use sub-agents to investigate and fix each issue separately.


<file name="packages/plugin/src/hooks/magic-context/hook-handlers.ts">

<violation number="1" location="packages/plugin/src/hooks/magic-context/hook-handlers.ts:537">
P2: `annotateEmptyTaskOutput` appends the "completed without a final text response" message to any `task` output whose string is empty or whitespace, even when it is not a completed task wrapper. The empty-string branch (`trim().length === 0`) falls through past the `EMPTY_COMPLETED_TASK_RESULT` guard, so a task that failed, aborted, or never produced a `<task state="completed">` wrapper is still labeled as a completed-but-empty subagent. That contradicts the stated scope (surface completed `task_result` that is empty) and feeds the model a misleading annotation. Make the guard consistent with the completed-task regex, or handle the bare-empty case separately.</violation>
</file>

<sub>Reply with feedback, questions, or to request a fix.

Re-trigger cubic</sub>

[cubic-dev-ai]

P2: annotateEmptyTaskOutput appends the "completed without a final text response" message to any task output whose string is empty or whitespace, even when it is not a completed task wrapper. The empty-string branch (trim().length === 0) falls through past the EMPTY_COMPLETED_TASK_RESULT guard, so a task that failed, aborted, or never produced a <task state="completed"> wrapper is still labeled as a completed-but-empty subagent. That contradicts the stated scope (surface completed task_result that is empty) and feeds the model a misleading annotation. Make the guard consistent with the completed-task regex, or handle the bare-empty case separately.

Prompt for AI agents

Check if this issue is valid — if so, understand the root cause and fix it. At packages/plugin/src/hooks/magic-context/hook-handlers.ts, line 537:

<comment>`annotateEmptyTaskOutput` appends the "completed without a final text response" message to any `task` output whose string is empty or whitespace, even when it is not a completed task wrapper. The empty-string branch (`trim().length === 0`) falls through past the `EMPTY_COMPLETED_TASK_RESULT` guard, so a task that failed, aborted, or never produced a `<task state="completed">` wrapper is still labeled as a completed-but-empty subagent. That contradicts the stated scope (surface completed `task_result` that is empty) and feeds the model a misleading annotation. Make the guard consistent with the completed-task regex, or handle the bare-empty case separately.</comment>

<file context>
@@ -533,6 +534,7 @@ export function createToolExecuteAfterHook(args: {
         // boundary. The queue helper re-checks the read-only mid-turn signal,
         // so this is a no-op until the assistant is actually idle.
         await flushIgnoredMessages(typedInput.sessionID);
+        annotateEmptyTaskOutput(typedInput.tool, output);
 
         if (typedInput.tool === "ctx_reduce") {
</file context>