feat(prove-it-works): add prove-it-works guardrail 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": "prove-it-works",
+      "description": "Guardrail that verifies task output against the real artifact before declaring done, not proxies or self-reports",
+      "source": "./plugins/prove-it-works",
+      "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.
 
+### prove-it-works
+
+Guardrail skill: verify every task output against the real artifact, not proxies or self-reports.
+
+**Skills:**
+
+- `prove-it-works` - Verify against the real artifact (run the feature, read the actual value, inspect the diff), not a proxy, self-report, or "it compiles"
+
 ## Plugin Structure
 
 Each plugin follows the Factory plugin format:

plugins/prove-it-works/.factory-plugin/plugin.json

@@ -0,0 +1,8 @@
+{
+  "name": "prove-it-works",
+  "description": "Guardrail that verifies task output against the real artifact before declaring done, not proxies or self-reports",
+  "author": {
+    "name": "yifu zuo",
+    "email": "yzuo.2019@gmail.com"
+  }
+}

plugins/prove-it-works/README.md

@@ -0,0 +1,9 @@
+# prove-it-works
+
+Behavioral guardrail: verify every task output against the real artifact before declaring done.
+
+**Skills:**
+
+- `prove-it-works` - Verify against the real artifact (run the feature, read the actual value, inspect the diff), not a proxy, self-report, or "it compiles"
+
+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/prove-it-works/skills/prove-it-works/SKILL.md

@@ -0,0 +1,21 @@
+---
+name: prove-it-works
+description: "Apply after completing a task, before declaring done. Verify against the real artifact (run the feature, read the actual value, inspect the diff), not a proxy, self-report, or 'it compiles.'"
+---
+
+# Prove It Works
+
+Verify every task output by checking the real thing directly. Do not infer from proxies, self-reports, or "it compiles."
+
+**Why:** Unverified work has unknown correctness. Indirect verification (file mtimes, output freshness, agent self-reports, cached screenshots) feels cheaper than direct observation. Acting on a wrong inference costs far more than checking the source.
+
+Check the real thing, not a proxy:
+- Check process liveness directly, not indirectly through derived state
+- Read the actual value, not a cached or derived representation
+- When verification fails, suspect the observation method before suspecting the system
+
+## Script the check when you can
+
+The strongest proof is a deterministic script that re-runs the same comparison, not a one-time eyeball. Write the script, run it, and keep its output as an artifact a reviewer can re-run instead of trusting your word.
+
+Keep the artifact visible for the human. Commit it only for large or complex work where the trail has to be auditable later, like a big port or migration (the show-me-your-work skill).

skills/prove-it-works

@@ -0,0 +1 @@
+../plugins/prove-it-works/skills/prove-it-works