refactor(chat): extract pure utility functions

[steebchen]

Summary

• Extract mightBeCompleteJson function to tools/might-be-complete-json.ts - JSON bracket balance heuristic for SSE parsing optimization
• Extract messagesContainImages function to tools/messages-contain-images.ts - checks messages for vision content
• Extract countInputImages function to tools/count-input-images.ts - counts images for Gemini cost calculation

This is Phase 1 of the chat.ts modularization effort. These are pure utility functions with zero external dependencies, making them easy to test and maintain.

Net change: -95 lines from chat.ts (103 removed, 8 added for imports)

Test plan

• pnpm format - passed
• pnpm build - passed
• pnpm test:unit - all 376 tests passed

🤖 Generated with Claude Code

Summary by CodeRabbit

• Refactor
  • Improved internal image detection and counting and added a lightweight JSON-completeness check to streamline message handling and parsing.
  • No user-facing behavior changes expected; these updates reduce internal complexity and improve reliability for messages that include images or JSON-like content.

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[coderabbitai]

Walkthrough

Extracts image- and JSON-related helpers from apps/gateway/src/chat/chat.ts into three new utility modules and updates chat.ts to import and use countInputImages, messagesContainImages, and mightBeCompleteJson, replacing the previous in-file image-counting and JSON heuristics.

Changes

Cohort / File(s)	Summary
Main chat update apps/gateway/src/chat/chat.ts	Removed in-file IMAGE_URL_PATTERN and manual image-counting/maybe-JSON helpers; added imports for countInputImages, messagesContainImages, and mightBeCompleteJson; delegates image counting and image-detection decisions to new utilities.
New utilities apps/gateway/src/chat/tools/count-input-images.ts, apps/gateway/src/chat/tools/messages-contain-images.ts, apps/gateway/src/chat/tools/might-be-complete-json.ts	Adds countInputImages(messages) (counts image_url parts and URLs in text using a shared RegExp), messagesContainImages(messages) (detects any image content parts), and mightBeCompleteJson(str) (lightweight brace/bracket balance heuristic).

Estimated code review effort

🎯 3 (Moderate) | ⏱️ ~20 minutes

Possibly related PRs

• feat: add input image counting for cost calculations #1271 — Modifies image-counting in apps/gateway/src/chat/chat.ts and wires input image counts into cost calculations.
• perf(gateway): optimize CPU-intensive code paths #1530 — Introduced original SSE/JSON completeness heuristic and image-detection code paths that were later extracted.
• refactor(chat): modularize chat handler with incremental modules #1537 — Refactors chat.ts by extracting various in-file helpers into separate tool modules (related extraction pattern).

Suggested labels

auto-merge

🚥 Pre-merge checks | ✅ 3

✅ Passed checks (3 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title 'refactor(chat): extract pure utility functions' accurately describes the main change: extracting three utility functions from chat.ts into separate modules.
Docstring Coverage	✅ Passed	Docstring coverage is 100.00% which is sufficient. The required threshold is 80.00%.

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✨ Finishing touches

• 📝 Generate docstrings

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Post copyable unit tests in a comment
• Commit unit tests in branch steebchen/chat-phase1-utilities

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