Add a tool-less Drupal Canvas Agent that answers general questions and names...

Description

Adds the canvas_agent ai_agent config entity to canvas_dev_ai, labelled "Drupal Canvas Agent". It answers general questions about Canvas and names the Tool that performs a task. It carries no tools.

Adds a [canvas_dev_ai:available_tools] token. It renders the Tools from canvas_dev_ai.settings, using the label and description of each ai_agent. CanvasDevAiHooks builds that list once, for both the JavaScript settings and the token, so the chat and the system prompt cannot describe the Tools differently, and the prompt cannot name a Tool that is not offered.

Two deliberate deviations from the issue:

1. main_agent is unchanged, so the agent is not selectable or active yet. Per the issue discussion, this MR creates the agent only, and setting main_agent moves to a follow-up.
2. The token reads canvas_dev_ai.settings in hook_tokens() rather than taking a context from CanvasDevAiBuilder::buildTokenContexts(). This also resolves the token outside a chat request, so the stored prompt never renders raw. Happy to move it to buildTokenContexts() to match the available_regions precedent if you prefer.

What changed

modules/canvas_dev_ai/config/install/ai_agents.ai_agent.canvas_agent.yml (new) — the agent. Empty tools, orchestration_agent: false, max_loops: 1. The prompt covers what Canvas does, which Tool to select, where Tools are enabled, and points at the documentation when it does not know. dependencies.enforced.module is canvas_dev_ai, so uninstalling the feature flag removes the agent with it.

modules/canvas_dev_ai/src/Hook/CanvasDevAiHooks.php — adds hook_token_info() and hook_tokens() for [canvas_dev_ai:available_tools], and extracts getToolDescriptors(). The JavaScript settings and the token now build the same list from the same method, so the chat and the prompt cannot describe a Tool differently. jsSettingsAlter() behaviour is unchanged, including omitting the key entirely when no Tool is selected.

hook_tokens() takes BubbleableMetadata and bubbles canvas_dev_ai.settings plus each offered agent as cacheable dependencies. testAvailableToolsToken and testAvailableToolsTokenWithoutTools assert the bubbled cache tags.

Behaviour

the ### Available Tools section of the rendered prompt, observed on a site via AiAgentEntityWrapper::applyTokens():

canvas_dev_ai.settings tools	Rendered section
canvas_ai_orchestrator, canvas_page_builder_agent	both, as * **<label>**: <description>
canvas_component_agent	that one only

Labels and descriptions come from the ai_agent entities, not from config, so a Tool cannot be described one way in the chat and another in the prompt.

Tests

CanvasDevAiAgentSelectionTest (+4 cases): the agent installs, lists no tools, is not itself offered as a Tool, is removed on uninstall, and the token renders the configured Tools — including the empty case, where an unreplaced token would otherwise reach the prompt as literal text.

Suite: 9 → 13 tests across the two files, 0 failures

Verification

• phpunit — 13 tests, 0 failures locally; CI green on 11.3 and 11.4 (Unit, Kernel, Functional)
• phpcs — clean on all three files
• phpstan — no errors on all three files
• cspell — clean
• Live check on an installed site: the token resolves through applyTokens() and tracks config changes

Two choices to confirm

main_agent is unchanged. The issue says to set it, superseding what #3591919 (closed) ships. Per the issue discussion this MR creates the agent only, and main_agent moves to a follow-up — so the agent is not selectable or active yet. CanvasDevAiAgentSelectionForm::SELECTABLE_AGENTS is untouched for the same reason.

The token reads config in hook_tokens() rather than taking a context from CanvasDevAiBuilder::buildTokenContexts(), as the issue specifies. This also resolves the token outside a chat request, so the stored prompt never renders raw, and it keeps this MR out of CanvasDevAiBuilder. Happy to move it to match the available_regions precedent if you prefer.

Closes #3591924