feat(tools): progressive tool disclosure for MCP and plugin tools

Adds Tool Search, a structured-tools progressive-disclosure layer that
replaces MCP and non-core plugin tools in the model-visible tools array
with three bridge tools (tool_search / tool_describe / tool_call) when
the deferrable surface would consume more than a configurable percentage
of the active model's context window. Core Hermes tools are never deferred.

Default mode is 'auto' with a 10% context threshold, so small toolsets
pay no overhead. Set tools.tool_search.enabled to 'on' to force or 'off'
to disable.

Design carefully reflects the OpenClaw production failure modes
documented in the openclaw-tool-search-report:

  - Core tools never defer (toolsets._HERMES_CORE_TOOLS). Addresses the
    'tools silently missing from isolated cron turns' regression class
    (openclaw#84141) by construction: there is no code path that can
    drop a core tool.
  - Catalog is stateless across turns — rebuilt from the live tool-defs
    list on every assembly. No session-keyed Map that can drift out of
    sync with the registry.
  - tool_call unwraps the bridge call before any hook fires, so plugin
    pre/post hooks, guardrails, approval flows, and the activity feed
    all see the underlying tool name, not the bridge (addresses
    openclaw#85588 and the verbose-mode complaint on openclaw#79823).
  - The unwrap happens in both the parallel and sequential paths of
    agent/tool_executor.py and also in handle_function_call, so direct
    callers (sandboxed code, eval harnesses) are covered too.
  - Bridge tools cannot invoke each other (recursion guard) and cannot
    invoke core tools (those must be called directly).
  - Tools mode only — no JS-sandbox code-mode. Keeps the surface small.
  - Token estimation via cheap char/4 heuristic; precision isn't needed
    for the threshold decision.

Files:
  - tools/tool_search.py — new module (BM25 retrieval, classification,
    threshold gate, bridge dispatch, unwrap helper).
  - tests/tools/test_tool_search.py — 35 tests including the OpenClaw
    #84141 regression guard.
  - model_tools.py — wires assembly into _compute_tool_definitions as the
    final step, adds skip_tool_search_assembly kwarg so the bridge can
    see the real catalog, dispatches the three bridge tools.
  - agent/tool_executor.py — unwraps tool_call in both parallel and
    sequential parsing loops so checkpointing, guardrails, plugin hooks,
    and tool-progress callbacks all observe the underlying tool name.
  - hermes_cli/config.py — DEFAULT_CONFIG['tools']['tool_search'] block.
  - website/docs/user-guide/features/tool-search.md — user docs.

Validation:
  - 35/35 new tests pass.
  - Existing tool/registry/model_tools/config/coercion/executor tests
    (82 + 74 + small adjacents) green.
  - Live E2E: 20 fake MCP tools registered, get_tool_definitions returns
    3 bridges, tool_search returns top 3 hits, tool_describe returns
    full schema, tool_call dispatches to the real underlying handler
    and the underlying result is what the model sees.
  - Reserved-name recursion guard verified live.
  - Core-tool refusal via tool_call verified live.

hermes_cli/config.py

@@ -1785,6 +1785,38 @@ DEFAULT_CONFIG = {
         "mode": "project",
     },
 
+    # Tool Search (progressive disclosure for large tool surfaces).
+    # When the model is connected to many MCP servers or non-core plugin
+    # tools, their JSON schemas can consume a substantial fraction of the
+    # context window on every turn. When enabled, those tools are replaced
+    # in the model-facing tools array with three bridge tools —
+    # tool_search / tool_describe / tool_call — and surfaced on demand.
+    #
+    # Core Hermes tools (terminal, read_file, write_file, patch,
+    # search_files, todo, memory, browser_*, etc.) are NEVER deferred.
+    # See tools/tool_search.py for full design notes and the
+    # openclaw-tool-search-report PDF in this PR for the rationale.
+    "tools": {
+        "tool_search": {
+            # "auto" (default) — activate only when deferrable tool schemas
+            #   exceed ``threshold_pct`` of the active model's context length,
+            #   so small toolsets pay no overhead.
+            # "on"  — always activate when there is at least one deferrable
+            #   tool. Use when you have many MCP servers and want maximum
+            #   token reduction unconditionally.
+            # "off" — disable entirely. Tools-array assembly is a pass-through.
+            "enabled": "auto",
+            # Percentage of context length at which "auto" mode kicks in.
+            # 10 matches the Claude Code default. Range 0..100.
+            "threshold_pct": 10,
+            # When the model calls tool_search without a ``limit`` argument,
+            # how many hits to return. Range 1..max_search_limit.
+            "search_default_limit": 5,
+            # Hard upper bound the model can request via ``limit``. Range 1..50.
+            "max_search_limit": 20,
+        },
+    },
+
     # Logging — controls file logging to ~/.hermes/logs/.
     # agent.log captures INFO+ (all agent activity); errors.log captures WARNING+.
     "logging": {