Junie cli incorrect session ID reported by --output-format json

# What
```
◉ nora[v0.5.3] 📁 projects (222) ❯ junie "do nothing and exit" --output-format=json
{"sessionId":"session-260408-000616-51s5","taskName":"No-Operation Exit Task","result":"The issue description requested to do nothing and exit, which has been fulfilled.","changes":[],"llmUsage":[{"model":"gemini-3-flash-preview","calls":1,"cost":0.003116,"inputTokens":5476,"cacheInputTokens":0,"cacheCreateTokens":0,"outputTokens":126},{"model":"gpt-5-2025-08-07","calls":1,"cost":0.0015325,"inputTokens":554,"cacheInputTokens":0,"cacheCreateTokens":0,"outputTokens":84},{"model":"gpt-4.1-2025-04-14","calls":1,"cost":9.2E-4,"inputTokens":192,"cacheInputTokens":1024,"cacheCreateTokens":0,"outputTokens":3},{"model":"gpt-4.1-mini-2025-04-14","calls":3,"cost":2.7519999999999997E-4,"inputTokens":612,"cacheInputTokens":0,"cacheCreateTokens":0,"outputTokens":19}]}
◉ nora[v0.5.3] 📁 projects (222) ❯ tail -n 1 ~/.junie/sessions/index.jsonl
{"sessionId":"session-260408-000616-1lkd","createdAt":1775570776078,"updatedAt":1775570779787,"projectDir":"/Users/simonmittag/projects","taskName":"No-Operation Exit Task"}
```

Junie reports a different sessonID to the one in the sessions log. I can't resume the sessionID junie returns because it doesn't exist. I need the cli to append to a previous session to preserve context

Reproduce the issue with `junie "do nothing and exit" --output-format=json`, then compare its reported sessionId with the last entry in `~/.junie/sessions/index.jsonl`. Trace the session creation and JSON output paths; done means the reported ID matches the sessions log and the session can be resumed to preserve context.

Written by the indexing model from the issue text.