feat: carry selected excerpt through composer integration references

[adriandemian]

Summary

Added support for carrying user-selected excerpt text from artifact surfaces (tickets, PRs, Granola notes) through the chat composer into agent prompt expansion. Three new optional fields on ComposerIntegrationReference: selectedExcerpt, selectedSourcePath, and selectedRangeLabel.

Excerpt text is appended to the expanded prompt even when no full-expansion service is available for that provider (e.g., ClickUp), and is rendered as a clearly labeled <selected_context> fence with fully escaped content to prevent injection.

User Impact

Agents can now see relevant context the user highlights from artifact surfaces without relying on provider expansion services to be wired. The selected text is marked as untrusted external context and never treated as instructions.

Technical Context

Frontend (frontend/src/api/chat.ts, frontend/src/components/agents/composer/agentComposerCore.ts):

• Three optional fields on ComposerIntegrationReference
• Normalization with bounds (COMPOSER_SELECTED_EXCERPT_MAX_LENGTH = 4000) and safety checks in normalizeComposerIntegrationReferences

Backend (src-tauri/src/domain/services/message_queue.rs):

• Struct fields with Default derive added; all existing literals updated

Expansion (src-tauri/src/application/integration_reference_expansion.rs):

• New append_selected_excerpts_for_prompt() appends excerpts after standard provider expansions, remaining within MAX_TOTAL_INTEGRATION_REFERENCE_BYTES budget
• format_selected_excerpt_block() renders <selected_context provider="..." kind="..." id="..." source="..." range="..."> fence with every value escaped via escape_attr() (body and attributes both escaped)
• safe_selected_attribute_value() validates selected_source_path and selected_range_label, dropping values with null bytes or newlines
• clamp_selected_excerpt() truncates on a UTF-8 character boundary (server-side max 16 KiB, matching MAX_SELECTED_EXCERPT_BYTES)
• Fold-in: excerpts skip attachment for references already marked BudgetExceeded during the expansion phase

Tests: Comprehensive coverage added to integration_reference_expansion_tests.rs (body injection, attribute breakout, newline filtering, character-boundary clamping, budget interaction); mechanical struct-literal updates across ~23 test files.

Risks / Follow-Ups

• Frontend and backend excerpt limits differ (4 KB vs 16 KB) intentionally: frontend clamps input, backend clamps render. No truncation surprise, but worth awareness.
• Excerpt body is marked untrusted external context in the prompt; agents should not execute or treat as instructions.
• User-facing UI surfaces for selecting and attaching excerpts (from tickets, PRs, Granola) are follow-up work per the original goal statement.

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Generated by RalphX

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