Add AI chat create_workspace_tab tool and cross-tab source access

[knightedcodemonkey]

Enable AI chat to create new workspace tabs (for example, styles tabs) and support cross-tab workflows where the user references a different tab than the active one.

Problem
Current AI chat flow can update existing tabs via propose_editor_update, but it cannot create tabs.
Requests like “add a new styles tab that colors paragraphs from src/components/status.tsx” are not fully satisfiable unless the target source tab is active or manually pasted into chat.

Goals

1. Add create_workspace_tab tool support in chat.
2. Keep propose_editor_update focused on updating existing tab content.
3. Preserve existing payload size/summarization protections.
4. Keep behavior mode-aware (DOM/React and style dialect policies already in place).

Non-goals

1. Multi-tab creation in one call.
2. Automatic framework/style dialect conversion.
3. Reworking existing workspace tab architecture.

Proposed Tool Contract
Tool name: create_workspace_tab

Parameters

1. path (string, required): normalized workspace-relative path for new tab.
2. language (string, required): tab language/dialect (for example javascript-jsx, css, less, sass, module).
3. initialContent (string, optional): initial source content.
4. activate (boolean, optional): whether to switch to new tab immediately.

Validation rules

1. Reject duplicate path collisions.
2. Normalize path consistently with existing tab helpers.
3. Reject unsupported/empty language values.
4. Return created tab id, name, path, language.

Follow-up for cross-tab context
Implement one of:

1. Send all tabs option in chat drawer, or
2. read_workspace_tab tool (id/path based) so model can pull source tab content explicitly.

Acceptance Criteria

1. AI can create a new styles tab through chat using create_workspace_tab.
2. Created tab appears in workspace tabs UI and persists via workspace save flow.
3. Existing propose_editor_update still updates by tab id/path.
4. No regression in chat payload byte budget and summarization behavior.
5. DOM mode guidance and style dialect guidance remain intact in system prompt context.
6. Playwright coverage added for:
7. Tool-call-driven tab creation success.
8. Duplicate path rejection handling.
9. Cross-tab request scenario with either Send all tabs or read_workspace_tab.

Suggested implementation touchpoints

1. proposals.js
2. drawer.js
3. app.js
4. github-workflows.js
5. github-workflows-setup.js
6. github-byot-ai.spec.ts

Risks / considerations

1. Avoid ambiguous target/path behavior between create and update tools.
2. Prevent invalid or unsafe paths.
3. Keep tool semantics simple and explicit (create vs update split).