Why

The frontend parseSpec function in dashboard/dist/index.js parses OpenSpec spec markdown into structured data (title, purpose, requirements with scenarios). This logic exists only in JavaScript — the Python backend and agent tools can't use it. Meanwhile, the dashboard's spec diff is line-level unified diff (difflib.unified_diff), which shows what text changed but not what requirements or scenarios changed. Agents have no way to get a structured delta at all — they must read two full specs and mentally diff them.

What Changes

Extract the spec parser into a shared Python function, build a semantic diff function on top of it, and expose it as a new openspec_spec_diff agent tool. The tool returns a structured JSON delta at the requirement/scenario level (added, modified, removed, unchanged) plus a unified line diff as a fallback field. Filesystem-backed — works without the OpenSpec CLI binary, same as the idea and change lifecycle tools.

Capabilities

New Capabilities

• semantic-spec-diff: Python spec parser, semantic diff function, and openspec_spec_diff agent tool for comparing specs at the requirement/scenario level

Modified Capabilities

• agent-tools: New openspec_spec_diff tool added to the plugin's registered tools, filesystem-backed (always available, no CLI gating)

Impact

• tools.py — new _parse_spec(), _semantic_spec_diff(), and openspec_spec_diff() functions
• schemas.py — new OPENSPEC_SPEC_DIFF schema
• __init__.py — register the new tool (filesystem-backed, no check_fn)
• plugin.yaml — add openspec_spec_diff to provides_tools
• tests/ — new test file for parser, diff, and tool handler