Fix sessionID navigation by using guaranteed ToolPart.sessionID field

[Copilot]

The sidebar's subagent navigation was broken due to checking non-existent metadata fields instead of using the guaranteed sessionID field from ToolPart.

Changes

• Replace dual-check pattern part.metadata?.sessionId ?? stateMetadata?.sessionId with direct part.sessionID access
• Remove incorrect string | undefined type cast (field is guaranteed by Zod schema)
• Remove conditional navigation check since sessionID is always present

// Before: checking non-existent fields
const stateMetadata = (part.state as { metadata?: Record<string, unknown> }).metadata
const sessionId = (part.metadata?.sessionId ?? stateMetadata?.sessionId) as string | undefined
onMouseDown={() => {
  if (sessionId) route.navigate({ type: "session", sessionID: sessionId })
}}

// After: using guaranteed field
const sessionId = part.sessionID
onMouseDown={() => {
  route.navigate({ type: "session", sessionID: sessionId })
}}

The ToolPart type inherits sessionID: string from its base schema, making it always available.

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[chatgpt-codex-connector]

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[chatgpt-codex-connector]

Use subagent metadata sessionId for navigation

Clicking a subagent entry now calls route.navigate with sessionId sourced from part.sessionID, but every task tool part in this list belongs to the current session so that value just reloads the session you are already viewing. The Task tool writes the subagent’s target session into state.metadata.sessionId when it creates or updates the subagent task (packages/opencode/src/tool/task.ts lines 57-62, 79-84, 135-139), so this change makes subagent sessions unreachable from the sidebar.

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