TUI crashes with 'undefined is not an object' when continuing session via -s flag #6887

Bug Description

Running opencode -s <session_id> crashes with:

TypeError: undefined is not an object (evaluating 'session().parentID')

Reproduction Steps

1. List sessions: opencode session (or via session_list API)
2. Pick a valid session ID
3. Run: opencode -s ses_4749abd4effe7hNsT4YSvK3ZgJ
4. TUI crashes immediately

Root Cause

The console shows the actual error before the crash:

[LOG] 'navigate' { type: 'session', sessionID: 'ses_4749abd4effe7hNsT4YSvK3ZgJ' }
[ERROR] Error: Unexpected end of JSON input
    SyntaxError: Unexpected end of JSON input
        at <parse> (:0)
        at json (unknown)
        at <anonymous> (../sdk/js/src/v2/gen/client/client.gen.ts:167:33)

The session.get API call returns an empty/malformed JSON response, causing JSON.parse to fail. The TUI then tries to render with session() === undefined, crashes on session().parentID access.

Expected Behavior

Should either:

1. Return valid JSON from the session.get API
2. Gracefully handle the error and show "Session not found" message

Environment

• opencode version: 1.1.1
• OS: macOS (darwin arm64)

Additional Context

The session DOES exist in the database (verified via session_info API which returns metadata correctly). The issue appears to be in the HTTP API layer or JSON serialization.