feat: Gemini infographic generation service (Task 4 — Imagen 4 Fast)

[codercatdev]

Task 4: Gemini Infographic Generation Service

Replaces closed PR #626 (which had a scope violation — included @research's gemini-research.ts from sandbox contamination).

Single file: lib/services/gemini-infographics.ts (~280 lines)

API Surface

Function	Purpose
generateInfographic(request, model?)	Generate a single infographic image via Imagen
generateInfographicBatch(requests, options?)	Generate multiple infographics with per-item error handling
generateInfographicsForTopic(topic, briefing?)	Main entry point for Sprint 3 — reads instructions from contentConfig.infographicInstructions, generates all infographics with deterministic seeds
buildInfographicPrompt(topic, style?)	Build a brand-consistent prompt from a topic string

Config Integration

• Model: pipelineConfig.infographicModel (default: imagen-4-fast, $0.02/image)
• Instructions: contentConfig.infographicInstructions (default: 5 blueprint-style prompts)
• Both use getConfigValue() with env var fallbacks

Key Features

• Deterministic seeds from topic + index hash — same topic always produces same seeds for brand consistency
• Fault isolation — each image in its own try/catch, failures collected in errors array
• Lazy SDK init — GoogleGenAI client created on first use, not at import time
• Blueprint-style defaults — 5 hand-drawn/whiteboard prompts matching the CodingCat.dev brand spec
• 16:9 aspect ratio default — matches video pipeline output

Cost

$0.02/image × 5 instructions = **$0.10 per topic**

Types Exported

InfographicResult, InfographicRequest, InfographicBatchOptions, InfographicBatchResult

Scope

✅ Only lib/services/gemini-infographics.ts — no other files touched.

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