feat(subtract-before-you-add): add subtract-before-you-add skill plugin

.factory-plugin/marketplace.json

@@ -53,6 +53,12 @@
       "description": "Pull request lifecycle skills: create PRs with consistent conventions and follow up on them until merge-ready",
       "source": "./plugins/code-review",
       "category": "productivity"
+    },
+    {
+      "name": "subtract-before-you-add",
+      "description": "Simplification guardrail: sequence removal before construction when evolving a system",
+      "source": "./plugins/subtract-before-you-add",
+      "category": "quality"
     }
   ]
 }

README.md

@@ -96,6 +96,14 @@ Skills for continuous learning and improvement.
 
 Autonomous experiment loop for optimization research. Try an idea, measure it, keep what works, discard what doesn't, repeat. Works standalone or as a mission worker.
 
+### subtract-before-you-add
+
+Simplification guardrail: when evolving a system, remove complexity first, then build.
+
+**Skills:**
+
+- `subtract-before-you-add` - Remove dead code, redundant validators, and stub references first, then build on the simpler base
+
 ## Plugin Structure
 
 Each plugin follows the Factory plugin format:

plugins/subtract-before-you-add/.factory-plugin/plugin.json

@@ -0,0 +1,8 @@
+{
+  "name": "subtract-before-you-add",
+  "description": "Simplification guardrail: sequence removal before construction when evolving a system",
+  "author": {
+    "name": "yifu zuo",
+    "email": "yzuo.2019@gmail.com"
+  }
+}

plugins/subtract-before-you-add/README.md

@@ -0,0 +1,9 @@
+# subtract-before-you-add
+
+Simplification guardrail: when evolving a system, remove complexity first, then build.
+
+**Skills:**
+
+- `subtract-before-you-add` - Remove dead code, redundant validators, and stub references first, then build on the simpler base
+
+Adapted from the pstack skills by Lauren Tan ([cursor/plugins](https://github.com/cursor/plugins), MIT License), with Cursor-specific tooling removed and Droid conventions applied.

plugins/subtract-before-you-add/skills/subtract-before-you-add/SKILL.md

@@ -0,0 +1,17 @@
+---
+name: subtract-before-you-add
+description: "Apply when sequencing an addition, refactor, or rewrite. Remove dead code, redundant validators, and stub references first, then build on the simpler base."
+---
+
+# Subtract Before You Add
+
+When evolving a system, remove complexity first, then build. Default to subtraction.
+
+Make simplification a continual investment. Leave the design slightly simpler and more capable behind the same or smaller surface than you found it.
+
+- Sequence removal before construction
+- Cut before you polish (get to the minimum before investing in quality)
+- Design for observed usage, not speculative edge cases
+- No speculative validators, parsers, or guards beyond what the spec demands
+- Simplify prompts (remove redundant instructions, excessive templates)
+- When a reference has no novel content, delete it rather than leaving a stub

skills/subtract-before-you-add

@@ -0,0 +1 @@
+../plugins/subtract-before-you-add/skills/subtract-before-you-add