mcp(refactor[display_message]): sharpen description + title for LLM discoverability

why: the name 'display_message' reads to an LLM like "show a
notification to the user" — the opposite of what the tool does
(evaluate a tmux format string and return the expanded value).
_BASE_INSTRUCTIONS already had corrective prose to compensate, which
is structural evidence the name is doing the wrong job. Rewording the
docstring summary and the MCP title lets the description carry the
meaning without touching the wire-name. A hard rename to
evaluate_format is deliberately deferred behind telemetry.

what:
- Rewrite the first sentence of display_message's docstring so
  FastMCP-indexed description leads with 'Evaluate a tmux format
  string... and return the expanded value.' — FastMCP pulls
  description from the docstring when no description= kwarg is given
  (fastmcp/tools/function_tool.py:225-227).
- Change the mcp.tool registration title from 'Display Message' to
  'Evaluate tmux Format String' in pane_tools/__init__.py.
- Refresh the corrective sentence in _BASE_INSTRUCTIONS to match the
  new wording and name-check the title shift.
- Complete the truncated '## Act' section in display-message.md and
  lead with the new framing; retitle the page to reflect the MCP
  title.

Author: tony

docs/tools/pane/display-message.md

@@ -1,11 +1,13 @@
-# Display message
+# Evaluate tmux format string (display_message)
 
 ```{fastmcp-tool} pane_tools.display_message
 ```
 
 **Use when** you need to query arbitrary tmux variables — zoom state, pane
 dead flag, client activity, or any `#{format}` string that isn't covered by
-other tools.
+other tools. Despite the historical name (`display_message` is the tmux verb
+it wraps), this tool does **not** display anything to the user; it expands
+the format string with `display-message -p` and returns the value.
 
 **Avoid when** a dedicated tool already provides the information — e.g. use
 {tooliconl}`snapshot-pane` for cursor position and mode, or
@@ -33,5 +35,3 @@ zoomed=0 dead=0
 
 ```{fastmcp-tool-input} pane_tools.display_message
 ```
-
-## Act

src/libtmux_mcp/server.py

@@ -59,9 +59,11 @@
     "READ TOOLS TO PREFER: snapshot_pane returns pane content plus "
     "cursor position, mode, and scroll state in one call — use it "
     "instead of capture_pane + get_pane_info when you need context. "
-    "display_message evaluates any tmux format string (e.g. "
-    "'#{pane_current_command}', '#{session_name}') against a target, "
-    "which is often cheaper than parsing captured output.\n\n"
+    "display_message evaluates a tmux format string (e.g. "
+    "'#{pane_current_command}', '#{session_name}') against a target "
+    "and returns the expanded value — cheaper than parsing captured "
+    "output. (The tool is named after the tmux 'display-message -p' "
+    "verb it wraps; its MCP title is 'Evaluate tmux Format String'.)\n\n"
     "WAIT, DON'T POLL: for 'run command, wait for output' workflows "
     "use wait_for_text (matches text/regex on a pane) or "
     "wait_for_content_change (waits for any change). These block "

src/libtmux_mcp/tools/pane_tools/__init__.py

@@ -120,9 +120,11 @@ def register(mcp: FastMCP) -> None:
     mcp.tool(title="Pipe Pane", annotations=ANNOTATIONS_SHELL, tags={TAG_MUTATING})(
         pipe_pane
     )
-    mcp.tool(title="Display Message", annotations=ANNOTATIONS_RO, tags={TAG_READONLY})(
-        display_message
-    )
+    mcp.tool(
+        title="Evaluate tmux Format String",
+        annotations=ANNOTATIONS_RO,
+        tags={TAG_READONLY},
+    )(display_message)
     mcp.tool(
         title="Enter Copy Mode",
         annotations=ANNOTATIONS_CREATE,

src/libtmux_mcp/tools/pane_tools/meta.py

@@ -26,10 +26,11 @@ def display_message(
     window_id: str | None = None,
     socket_name: str | None = None,
 ) -> str:
-    """Query tmux using a format string.
+    """Evaluate a tmux format string against a target and return the expanded value.
 
-    Expands tmux format variables against a target pane. Use this as a
-    generic introspection tool to query any tmux variable, e.g.
+    Read-only introspection tool — expands any tmux format variable
+    against a target pane and returns the substituted text. Use this
+    when no dedicated tool covers the field you want, e.g.
     '#{window_zoomed_flag}', '#{pane_dead}', '#{client_activity}'.
 
     Parameters