Add ctxguard: hook-enforced context sanitization

Keeps credentials, company names, personal names and PII out of the model's
context. Enforcement lives in Claude Code hooks rather than in instructions to
the agent: a skill alone cannot protect anything, because by the time the agent
reads a rule the surrounding context has already been sent.

Credentials are removed irreversibly and marked. Entities from a user-supplied
dictionary become stable aliases, rewritten back to real values on their way to
disk and to the shell, so code and commands referring to them still work.

Published from a clean tree; development history is not included.

.claude-plugin/marketplace.json

@@ -0,0 +1,17 @@
+{
+  "$schema": "https://anthropic.com/claude-code/marketplace.schema.json",
+  "name": "ctx-tools",
+  "description": "Claude Code plugins for keeping sensitive data out of the model's context",
+  "owner": {
+    "name": "A.Shakhmatov",
+    "email": "dev@shakhmatov.com"
+  },
+  "plugins": [
+    {
+      "name": "ctxguard",
+      "source": "./plugins/ctxguard",
+      "description": "Sanitizes the agent's context: blocks credentials and replaces company names, people and PII with stable reversible aliases before anything reaches the model",
+      "version": "1.0.4"
+    }
+  ]
+}