plat 429

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PLAT-429 — A Codex chat in Code said it could not open a panel because "the UI control tools aren't available"

Coordination	Value
State	fixed on main (skill and guidance wording); deploy pending
Severity	P3 (the agent refused a supported action until the owner asked "did you check the API spec")
Date	2026-10-04
Owner	coding-agent-bridge
Related	PLAT-396 (full mode), the workspace-ui feature

Problem

In a Code chat on Excellence with Codex (full native tools), asked to open the Costs panel, the agent replied: "I can't open it from this chat because the UI control tools aren't available here". The tools were available: the server registered list_ui_capabilities, get_ui_state and perform_ui_action for the session (the tool gate lists them), and after the owner asked "did you check the API spec" Codex found them through the API discovery tools.

Cause

A coding-CLI chat has only a few direct tools (here agent_browser, execute_shell_command, get_api_spec, search_tools); every other platform tool is reached through the API bridge (search_tools, then get_api_spec, then HTTP). The shared work-ui-control skill (rendered for Crew as work-ui-control and for Code as code-ui-control) said "use these only in a chat that actually exposes them" and never said how to reach them. Codex checked its direct tool list (ALL_TOOLS), found no match and concluded they were missing.

What a Code chat with Codex gets as its prompt

Codex receives the platform's prompt through the project's AGENTS.md (about 10 KB, delivered as the first user message and in world_state) next to Codex's own developer messages (about 7 KB plus a skills list). AGENTS.md does contain the bridge facts: an "IMPORTANT — bridge tool routing" block (direct runtime tools: search_tools, get_api_spec, execute_shell_command, agent_browser, read_image, read_skill; other tools are found with search_tools). The ambiguous line was in the product section "Platform actions": "Discover tools through the current runtime's tool search" (Crew: "Use the current runtime's tool discovery"). For Codex that reads as its own tool search (ALL_TOOLS), which is what it used.

Fix

The 2026-10-01 prompt reduction (DECISIONS "Keep prompt contracts upfront and load procedures through skills"; Code -21%, Crew Builder -40%, workflow chats about -40%) gave discovery ONE owner: mcpagent's runtime block "bridge tool routing" (coding_agent_bridge_routing_prompt.go: direct runtime tools, "find other tools with search_tools", schema and route via get_api_spec), with a short pointer in each product prompt. The failing text was a pointer that contradicted the owner. So the fix keeps one owner and only corrects the pointers, in as few words as possible:

• Owner (mcpagent, all CLIs): the sentence above, once.
• Code and Crew system prompts: "Find platform tools with search_tools (see bridge tool routing); a tool missing from your own tool list is not missing." (Code prompt 2076 -> 1826 bytes, Crew 4178 -> 3965, smaller than before the incident.)
• The shared work-ui-control skill (Crew and Code): two lines saying these are bridge tools found with search_tools(query="ui").
• Tests: TestCodePromptNamesTheBridgeToolDiscovery, TestCrewPromptNamesTheBridgeToolDiscovery and the skill expectations in product_config_test.go. A first version repeated the full explanation in four places (both prompts, the skill, the Workflow guidance); it was cut back to the pointers above because it went against "one owner for transport instructions".

What a Code chat with Codex gets as its prompt

Codex receives the platform's prompt through the project's AGENTS.md (about 10 KB, first user message and world_state) next to Codex's own developer messages. AGENTS.md holds the runtime block. The ambiguous pointer was in the product section "Platform actions" ("Discover tools through the current runtime's tool search"; Crew: "Use the current runtime's tool discovery"). For Codex that reads as its own tool search (ALL_TOOLS), which is what it used.

Review of the other prompts (2026-10-04)

Only the Code and Crew prompts used the ambiguous pointer. Video Studio and Dominion prompts refer to get_api_spec with exact tool names (the catalog of names is still provided there, as the reduction decision requires); the Workflow guidance templates and Relays rely on the runtime block; the only other "tool search" wording is about step tool selection in optimize-playbook.md, unrelated.

Left

• Deploy; then ask Codex, Claude and Muse in a Code chat to open the Costs panel and check each finds and calls perform_ui_action through the bridge.
• Relays has no contract of its own for these tools: it reuses the Workflow views, and its right panel (workflow panel on, files panel off) may not match them; not checked in the UI.
• Other platform tools have the same shape (a CLI that only checks its direct tool list will think they are missing); the general bridge guidance already says to use search_tools.