docs: add context-mode routing rules to CLAUDE.md

Add mandatory routing rules section for context-mode MCP plugin,
documenting blocked commands, redirected tools, tool selection
hierarchy, and output constraints.

CLAUDE.md

@@ -168,3 +168,78 @@ Check: `make check-version-refs`
 ---
 
 All actions modular and externally usable. No exceptions to any rule.
+
+## context-mode — MANDATORY routing rules
+
+You have context-mode MCP tools available. These rules are NOT optional — they protect your context window from flooding. A single unrouted command can dump 56 KB into context and waste the entire session.
+
+### BLOCKED commands — do NOT attempt these
+
+#### curl / wget — BLOCKED
+
+Any Bash command containing `curl` or `wget` is intercepted and replaced with an error message. Do NOT retry.
+Instead use:
+
+- `ctx_fetch_and_index(url, source)` to fetch and index web pages
+- `ctx_execute(language: "javascript", code: "const r = await fetch(...)")` to run HTTP calls in sandbox
+
+#### Inline HTTP — BLOCKED
+
+Any Bash command containing `fetch('http`, `requests.get(`, `requests.post(`, `http.get(`, or `http.request(` is intercepted and replaced with an error message. Do NOT retry with Bash.
+Instead use:
+
+- `ctx_execute(language, code)` to run HTTP calls in sandbox — only stdout enters context
+
+#### WebFetch — BLOCKED
+
+WebFetch calls are denied entirely. The URL is extracted and you are told to use `ctx_fetch_and_index` instead.
+Instead use:
+
+- `ctx_fetch_and_index(url, source)` then `ctx_search(queries)` to query the indexed content
+
+### REDIRECTED tools — use sandbox equivalents
+
+#### Bash (>20 lines output)
+
+Bash is ONLY for: `git`, `mkdir`, `rm`, `mv`, `cd`, `ls`, `npm install`, `pip install`, and other short-output commands.
+For everything else, use:
+
+- `ctx_batch_execute(commands, queries)` — run multiple commands + search in ONE call
+- `ctx_execute(language: "shell", code: "...")` — run in sandbox, only stdout enters context
+
+#### Read (for analysis)
+
+If you are reading a file to **Edit** it → Read is correct (Edit needs content in context).
+If you are reading to **analyze, explore, or summarize** → use `ctx_execute_file(path, language, code)` instead. Only your printed summary enters context. The raw file content stays in the sandbox.
+
+#### Grep (large results)
+
+Grep results can flood context. Use `ctx_execute(language: "shell", code: "grep ...")` to run searches in sandbox. Only your printed summary enters context.
+
+### Tool selection hierarchy
+
+1. **GATHER**: `ctx_batch_execute(commands, queries)` — Primary tool. Runs all commands, auto-indexes output, returns search results. ONE call replaces 30+ individual calls.
+2. **FOLLOW-UP**: `ctx_search(queries: ["q1", "q2", ...])` — Query indexed content. Pass ALL questions as array in ONE call.
+3. **PROCESSING**: `ctx_execute(language, code)` | `ctx_execute_file(path, language, code)` — Sandbox execution. Only stdout enters context.
+4. **WEB**: `ctx_fetch_and_index(url, source)` then `ctx_search(queries)` — Fetch, chunk, index, query. Raw HTML never enters context.
+5. **INDEX**: `ctx_index(content, source)` — Store content in FTS5 knowledge base for later search.
+
+### Subagent routing
+
+When spawning subagents (Agent/Task tool), the routing block is automatically injected into their prompt.
+Bash-type subagents are upgraded to general-purpose so they have access to MCP tools.
+You do NOT need to manually instruct subagents about context-mode.
+
+### Output constraints
+
+- Keep responses under 500 words.
+- Write artifacts (code, configs, PRDs) to FILES — never return them as inline text. Return only: file path + 1-line description.
+- When indexing content, use descriptive source labels so others can `ctx_search(source: "label")` later.
+
+### ctx commands
+
+| Command | Action |
+|---------|--------|
+| `ctx stats` | Call the `ctx_stats` MCP tool and display the full output verbatim |
+| `ctx doctor` | Call the `ctx_doctor` MCP tool, run the returned shell command, display as checklist |
+| `ctx upgrade` | Call the `ctx_upgrade` MCP tool, run the returned shell command, display as checklist |