GUI parity: extend --json stdio protocol with in-session control requests (model switch, compact, plan toggle, agent select)

[pranavp311]

Context

Building a Tauri/React GUI (codegraff-zig/gui) on top of a persistent graff --json session per conversation. Streaming (text/tool_call/tool_result/turn/error) works well.

Problem

The --json stdio protocol currently accepts only three request types — user, set_system_prompt, score (per --schema → protocol). Several GUI controls map to graff REPL commands that act on the live session and have no protocol equivalent, so a persistent --json session can't drive them:

• Model switch (/model): the GUI can only set the model at spawn (--model). Switching mid-conversation requires killing + respawning the child, which loses context.
• Compaction (/compact): the GUI can't compact the live session's context (today it shows only a cosmetic marker).
• Plan mode toggle (/plan): read-only mode can't be entered/exited per turn.
• Agent switch (/agents).

Proposal

Add request types to the stdio protocol (and mirror over serve), each acked with an event — same pattern as set_system_prompt:

{"type":"set_model","name":"deepseek-v4-pro"}   // -> {"type":"model","ok":true,"name":"..."}
{"type":"compact"}                               // -> compaction ack / turn
{"type":"set_mode","mode":"plan"|"normal"}       // -> {"type":"mode","ok":true,"mode":"..."}
{"type":"set_agent","id":"..."}                  // -> {"type":"agent","ok":true,"id":"..."}

Same KV-cache caveat as set_system_prompt applies (mutations at turn boundaries). Happy to implement once the shape is agreed.

[pranavp311]

Protocol shape I’m implementing for the live-session GUI controls:

{"type":"set_model","name":"<fuzzy name|provider|provider/model>"}
   -> {"type":"model","ok":true,"id":"<provider>","name":"<model>","context":N,"note":"<switch note>"}
   -> {"type":"error","message":"no key/login for ..."}

{"type":"compact"}
   -> {"type":"compact","ok":true,"chars":N}
   -> {"type":"error","message":"..."}

{"type":"set_mode","mode":"plan"|"normal"}
   -> {"type":"mode","ok":true,"mode":"plan"}

{"type":"set_agent","id":"<agent name>"}
   -> {"type":"agent","ok":true,"id":"reviewer","chars":N}
   -> {"type":"error","message":"unknown agent 'x' (see /agents)"}
{"type":"set_agent","id":""} // reset to base prompt

Two clarifications versus the issue draft:

1. set_agent is a main-session system-prompt swap: base main_system_prompt plus the selected persona prompt. Graff does not have a separate runtime “active agent” mode for the main session today.
2. set_mode is explicit (mode: "plan" | "normal") rather than a toggle so GUI state and harness state stay synchronized.

[pranavp311]

Implemented solution for issue #1 in the GUI review branch.

What changed

• Added JSON stdio control requests for live session model switching, compaction, plan/normal mode switching, and agent selection.
• Added explicit ack events for each control request so GUI callers can confirm success/failure without treating controls as user turns.
• Updated schema output so clients can discover the new request/event shapes.
• Made compaction JSON-safe by suppressing terminal-only output while --json is active and returning the compacted character count in the ack.
• Wired the Tauri GUI runtime to send the new control requests to the persistent graff --json session and persist per-conversation agent/plan state for fresh session spawns.

Implemented protocol

{"type":"set_model","name":"<fuzzy name|provider|provider/model>"}
  -> {"type":"model","ok":true,"id":"<provider>","name":"<model>","context":N,"note":"<switch note>"}

{"type":"compact"}
  -> {"type":"compact","ok":true,"chars":N}

{"type":"set_mode","mode":"plan"}
  -> {"type":"mode","ok":true,"mode":"plan"}

{"type":"set_agent","id":"forge"}
  -> {"type":"agent","ok":true,"id":"forge"}

All control requests return a type: "error" event with a descriptive message when validation or execution fails.

Verification run locally

/Users/pranavp/.local/zig/0.16.0/zig fmt --check src/main.zig
/Users/pranavp/.local/zig/0.16.0/zig build test
cargo check --manifest-path gui/src-tauri/Cargo.toml
npm test -- --runInBand

Result: all passed.

Co-Authored-By: blackfloofie-a codegraff agent 265516171+blackfloofie@users.noreply.github.com

[pranavp311]

Closed — all four protocol extensions (set_model, compact, set_mode, set_agent) are implemented in the harness, tested (scripts/test-json-controls.py), and wired through the Tauri bridge (send_control, acquire_session_io).