mcec: Instructions file for Codex

AGENTS.md: driving (and testing) MCEC with an agent

MCEC 3.0 (the Model Context Environment Controller) gives an AI agent eyes, hands, and a safe front door on Windows (Windows computer use, in the sense Claude, Codex, and similar agents use the term). This file is the self-reinforcing guidance loop: the canonical guidance an agent needs, plus the recipe to dogfood it (drive MCEC through its own MCP server) so the guidance stays honest. Each time MCEC changes, re-run the dogfood and refine the guidance below and in AgentServer.Instructions.

The built-in guidance (single source of truth)

The connect-time guidance an MCP client shows the model is authored in src/Agent/AgentInstructions.md. It is embedded into the exe at build time and returned in the MCP initialize response (result.instructions) via AgentServer.Instructions, which loads the embedded file and collapses each blank-line-separated paragraph to one line.

Work the loop observe → target → act → observe.

1. Target a window by window (title substring), process (name without .exe), className, or foreground:true. At least one is required; a call with no target fails by design.
2. Observe: query dumps the UI Automation tree (controlType, name, automationId, bounds, state, value; bounded by maxDepth and maxNodes); capture returns a PNG (renders composited WinUI/WPF surfaces correctly). Check results before trusting them: a capture with errorCategory: capture-blank is a black/empty frame (minimized/cloaked/occluded/locked session); restore or foreground the window and retry, don't trust the image; a capture-fallback warning means PrintWindow was refused and the picture may be wrong; a query with truncated:true (a tree-truncated warning) hit the node cap; raise maxNodes or target a deeper window. warnings are non-fatal; errorCategory tells you how to recover. (Shape: docs/agent_control.md and agent-tool-result.schema.json.)
3. Act: prefer invoke (by name/automationId/classname; action invoke|toggle|setvalue| setfocus|expand|collapse|select) over coordinate clicks. invoke fast-fails if the control isn't present (it does not wait), so find/wait-for the control first; an invoke that returns no-target means it hasn't appeared yet; wait-for it rather than retrying blindly. Use select for TabItem/ListItem/RadioButton. To drag (resize a window by its sizing border, move one by its title bar, or drag a slider/handle; no invoke for these), use the drag tool: give a from and to, each an element { by, value } or an absolute screen pixel { x, y }, plus optional path waypoints; the whole press-move-release is dispatched atomically (prefer it over hand-rolling mouse:lbd/mouse:mt/mouse:lbu, which can interleave with other input). To click a point invoke can't reach (a custom-drawn cell, a canvas/map coordinate, a bare pixel), use the click tool. Before firing an app's own keyboard shortcut at a specific surface (e.g. a MAUI GraphicsView), focus it first; keystrokes only reach the foreground window's focused control. send_command is the raw escape hatch for any other MCEC command (keystrokes, a single mouse action, launch). Re-query after acting; bounds have moved.
4. Verify with another query/capture.

Compose creatively. Many tasks have no single dedicated tool; build them from primitives. Launch an app with the launch tool (preferred). Use invoke action:select for tabs/list/radios. Drag/resize/move with the drag tool; switch a tab by invoke select or click; record a window by passing its query'd bounds as the record region; wait on window state with the windows tool + a timeout and a condition (appears/disappears/foreground). A capable agent uses the full command set; reach for a raw send_command before concluding something can't be done.

There is exactly one copy: edit that file. It is the observe → target → act → observe playbook (targeting; observation with query/capture/record/displays; invoke, drag, click, focus and send_command; the result envelope; creative composition of primitives; the on-screen overlay; and the security gates). Nothing here to keep in sync.