fix(app): port child-session navigation fix to V2

[opencode-agent]

Problem

In OpenCode V2, clicking a subagent/task invocation can appear to do nothing when the child session is not already present in the app session-list cache. The card has the correct child-session href and the child is available from the direct session endpoint, but the URL remains on the parent. This makes navigation cache-dependent and therefore intermittent.

Source: https://discord.com/channels/1391832426048651334/1447692703549755466/1523734996358009104

Root cause

origin/v2 still resolves target session lineage with a suspending createResource inside the Solid Router navigation transition. For an uncached child session, that suspends the transition before the URL commit.

dev already fixed this in commit 39dfbb53d016d50bb8d2113407b8e20c0bd800c7 / PR #34838 by resolving lineage imperatively outside the router transition. That commit also added subagent-child-navigation.spec.ts.

Verification

• Base tested: origin/v2 at 147da5d278a
• Repro: parent timeline contains a task card with a valid child-session href; /session omits the child while /session/:child resolves it. Clicking leaves the URL on the parent.
• Applying 39dfbb53d016d50bb8d2113407b8e20c0bd800c7 to V2 makes the exact regression test pass (1 passed, 8.3s).

Next step

Port/cherry-pick the app route fix and its regression coverage onto V2, resolving any branch drift.

[opencode-agent]

Closing as fixed on current origin/v2. The session route now uses createSessionLineage for target session resolution via the dev→v2 merge (commit 9e0d397, #35591), so uncached child-session navigation is no longer tied to the router transition cache.