libtmux_mcp.middleware.TailPreservingResponseLimitingMiddleware

Description#

FastMCP's stock ResponseLimitingMiddleware truncates the tail of the response (keeps the start, appends a suffix). That's exactly wrong for terminal scrollback, where the active shell prompt and most recent command output live at the bottom of the buffer. This subclass overrides _truncate_to_result to drop the head instead, prefixing a single truncation-header line so callers can detect the cap fired.

Used as a backstop for libtmux_mcp.tools.pane_tools.capture_pane, libtmux_mcp.tools.pane_tools.capture_since, libtmux_mcp.tools.pane_tools.snapshot_pane, and libtmux_mcp.tools.pane_tools.search_panes, plus libtmux_mcp.tools.buffer_tools.show_buffer. Per-tool caps at the tool layer fire first under normal operation; this middleware catches a missed bound within that configured high-volume set.

Error results keep their is_error flag through truncation. The stock truncation path rebuilds the result without it, which turns an oversized error (e.g. a validation message echoing a huge argument) into an apparent success — MCP clients then validate the truncated text against the tool's output schema and fail with a transport-level error instead of delivering the tool error. meta (error_type / expected / suggestion) already survives via the base class, and tail-preservation keeps the suggestion line, which sits at the end of the text.