[dezren39]

Fixes #505

Forking a child session laundered it out of ancestor governance: the projector inserts a fork with parent_id: null (keeping only fork_session_id and a copy of the source's own subagent_policy), and every governance walk followed parentID only — so a fork escaped every policy above its source, its own switchAgent/switchModel were unchecked (top-level gate), and its descendants were governed only by the copied policy. Spec specs/2026-10-25-subsession-model-governance.md §6.2 already decided the opposite: "Session.fork creates a child whose parent is the source session."

Shape (governance-link, projection untouched)

The fork stays projected top-level (parent_id still null, listing/projection unchanged); governance now treats the fork source as the fork's governance parent:

• packages/core/src/session/model-governance.ts — the assertAllowed ancestor walk follows parentID ?? fork.sessionID, so ancestor session policies above the source bind the fork, its switches (via the creation/fork checks that call it), and its descendants' creation.
• packages/core/src/session/session.ts — switchAgent/switchModel gate on the governance parent (parentID ?? fork.sessionID) instead of parentID alone, so a fork's own switches are checked against its source's chain; genuinely top-level sessions remain unchecked.
• packages/core/src/session/subagent-depth.ts — the depth walk follows the same link, so max_depth caps above the source bind the fork's subtree (a fork hop counts as one level, as a child would).

Tests

New regression test in packages/core/test/session-governance.test.ts: a grandchild is forked under a grandparent policy of test/haiku only — the fork (projected top-level, parentID undefined) cannot switchModel to test/opus, cannot launch children on test/opus, and can launch children on test/haiku. Existing fork governance tests (fork-of-policy-denied, permitted fork copies policy) and the session-governance suite run in CI.

Verification is CI-only per fleet policy; the unit suites on this PR are the evidence.

Queue task 2725.

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Files selected for processing: 4

• packages/core/src/session/model-governance.ts
• packages/core/src/session/session.ts
• packages/core/src/session/subagent-depth.ts
• packages/core/test/session-governance.test.ts

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[chatgpt-codex-connector]

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Review	Status	Commit	Review trigger
📝 Code Review	✅ Completed 2026-10-28T22:00:01.416079Z	72ceef6	PR opened

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[chatgpt-codex-connector]

Preserve fork governance when the source session is deleted

After a user forks a session and deletes the source, the surviving fork can no longer switch models or agents, create children, or be forked again: these operations now require loading the deleted source. Session.remove in packages/core/src/session.ts recursively removes only sessions returned by list({ parentID: sessionID }), and SessionStore.list filters on parent_id, so top-level-projected forks survive deletion with a dangling fork.sessionID. The new governance walks then fail with NotFoundError or Parent session not found, even when no model restrictions were configured. Coordinate source deletion with the new governance relationship so surviving forks retain usable, enforceable governance rather than depending on a row that can be removed.

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