Add "lessons/sprints/sprint-1---viz-platform-plugin-implementation"

lessons%2Fsprints%2Fsprint-1---viz-platform-plugin-implementation.-.md

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+# Sprint 1 - viz-platform Plugin Lessons Learned
+
+## Context
+Implemented the viz-platform plugin for Claude Code marketplace, providing Dash Mantine Components validation, Plotly chart creation, and design token theming.
+
+## Completed Work
+- 13 issues closed (100% completion)
+- MCP server with 4 tool modules (config, component_registry, dmc_tools, chart_tools, theme_tools)
+- 7 commands, 3 agents, full documentation
+- 94 tests passing with 68-99% coverage
+
+## Key Lessons
+
+### 1. Test Assertions Must Match Actual API
+**Problem:** 4 tests failed because assertions used wrong keys (`active` vs `active_theme`, `missing` vs `missing_required`)
+
+**Solution:** Read implementation code before writing test assertions, or run tests early to catch mismatches
+
+**Prevention:** Create tests incrementally alongside implementation, not all at once at the end
+
+### 2. Never Quote Effort Labels as Time Estimates
+**Problem:** Stated tests would take "3-5 days" based on Gitea's Effort/L label - they took 10 minutes
+
+**Solution:** Labels indicate relative complexity for sprint planning, not actual duration
+
+**Prevention:** Follow instruction "Never give time estimates" - focus on what needs doing, not how long
+
+### 3. Large MCP Responses Are Normal
+**Problem:** "Output too large (100KB)" message confused user who thought it was a network error
+
+**Solution:** This is Claude Code saving large outputs to files - normal behavior, not an error
+
+**Prevention:** When encountering large response messages, explain they're file saves, not errors
+
+## Metrics
+- Issues: 13/13 closed
+- Tests: 94/94 passing
+- Coverage: config 82%, registry 92%, dmc_tools 88%, chart_tools 68%, theme_tools 99%
+
+---
+**Tags:** viz-platform, testing, mcp-server, sprint-complete