[Bug]: ACP session/new returns different session ID than what's persisted to disk

[jcfs]

What happened?

When using auggie --acp mode, the session/new method returns a session ID that does not match
the session ID persisted to ~/.augment/sessions/.

For example:
• ACP session/new returns: bef591a3-cc2b-4d62-a037-4ea2f8d6a96d
• Session saved to disk as: ~/.augment/sessions/5eba0a8e-e930-4a0a-95c3-cf04c1d4607b.json
• The file ~/.augment/sessions/bef591a3-cc2b-4d62-a037-4ea2f8d6a96d.json does not exist

This makes it impossible for ACP clients to know the correct session ID for resuming sessions
via --resume.

What did you expect to happen?

The session ID returned by session/new should match the session ID persisted to disk, so ACP
clients can use it with --resume for session resumption.

Alternatively, there should be an ACP method (like session/load or session/info) to retrieve or
use the persisted session ID.

Steps to reproduce

1. Start auggie in ACP mode: auggie --acp

   2. Send initialize request:

{"jsonrpc":"2.0","id":1,"method":"initialize","params":{"protocolVersion":1,"clientInfo":{"nam
e":"test","version":"1.0"}}}

 3. Send session/new request:

{"jsonrpc":"2.0","id":2,"method":"session/new","params":{"cwd":"/tmp/test","mcpServers":[]}}

 4. Note the returned sessionId (e.g., bef591a3-cc2b-4d62-a037-4ea2f8d6a96d)

 5. Send a prompt and wait for completion:

{"jsonrpc":"2.0","id":3,"method":"session/prompt","params":{"sessionId":"bef591a3-cc2b-4d62-a0
37-4ea2f8d6a96d","prompt":[{"type":"text","text":"Say hello"}]}}

 6. After completion, check ~/.augment/sessions/:

ls ~/.augment/sessions/ | grep bef591a3

Returns nothing - file doesn't exist

ls -lt ~/.augment/sessions/ | head -2

Shows a NEW file with a DIFFERENT session ID was created

 7. Observed: The persisted session file has a different UUID than what ACP returned.

Auggie version

0.14.0

Request ID

N/A - this is reproducible on every ACP session

Environment details

Environment

 • OS: Linux (Ubuntu)
 • Shell: bash
 • Node.js: v23.11.0

Anything else we need to know?

• Attempting to use session/load returns "Method not found", so ACP clients cannot resume
sessions via ACP protocol
• The current workaround requires monitoring the filesystem for new files in
~/.augment/sessions/ to discover the persisted session ID, which is fragile
• Using --resume as a CLI flag does work correctly once you know the
persisted ID

Suggested solutions:
1. Make session/new return the same session ID that will be persisted to disk
2. Include the persisted session ID in the session/prompt response on end_turn
3. Implement session/load method in ACP mode