feat: add product capability planning lane

.agents/skills/product-capability/SKILL.md

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+---
+name: product-capability
+description: Translate PRD intent, roadmap asks, or product discussions into an implementation-ready capability plan that exposes constraints, invariants, interfaces, and unresolved decisions before multi-service work starts. Use when the user needs an ECC-native PRD-to-SRS lane instead of vague planning prose.
+origin: ECC
+---
+
+# Product Capability
+
+This skill turns product intent into explicit engineering constraints.
+
+Use it when the gap is not "what should we build?" but "what exactly must be true before implementation starts?"
+
+## When to Use
+
+- A PRD, roadmap item, discussion, or founder note exists, but the implementation constraints are still implicit
+- A feature crosses multiple services, repos, or teams and needs a capability contract before coding
+- Product intent is clear, but architecture, data, lifecycle, or policy implications are still fuzzy
+- Senior engineers keep restating the same hidden assumptions during review
+- You need a reusable artifact that can survive across harnesses and sessions
+
+## Canonical Artifact
+
+If the repo has a durable product-context file such as `PRODUCT.md`, `docs/product/`, or a program-spec directory, update it there.
+
+If no capability manifest exists yet, create one using the template at:
+
+- `docs/examples/product-capability-template.md`
+
+The goal is not to create another planning stack. The goal is to make hidden capability constraints durable and reusable.
+
+## Non-Negotiable Rules
+
+- Do not invent product truth. Mark unresolved questions explicitly.
+- Separate user-visible promises from implementation details.
+- Call out what is fixed policy, what is architecture preference, and what is still open.
+- If the request conflicts with existing repo constraints, say so clearly instead of smoothing it over.
+- Prefer one reusable capability artifact over scattered ad hoc notes.
+
+## Inputs
+
+Read only what is needed:
+
+1. Product intent
+   - issue, discussion, PRD, roadmap note, founder message
+2. Current architecture
+   - relevant repo docs, contracts, schemas, routes, existing workflows
+3. Existing capability context
+   - `PRODUCT.md`, design docs, RFCs, migration notes, operating-model docs
+4. Delivery constraints
+   - auth, billing, compliance, rollout, backwards compatibility, performance, review policy
+
+## Core Workflow
+
+### 1. Restate the capability
+
+Compress the ask into one precise statement:
+
+- who the user or operator is
+- what new capability exists after this ships
+- what outcome changes because of it
+
+If this statement is weak, the implementation will drift.
+
+### 2. Resolve capability constraints
+
+Extract the constraints that must hold before implementation:
+
+- business rules
+- scope boundaries
+- invariants
+- trust boundaries
+- data ownership
+- lifecycle transitions
+- rollout / migration requirements
+- failure and recovery expectations
+
+These are the things that often live only in senior-engineer memory.
+
+### 3. Define the implementation-facing contract
+
+Produce an SRS-style capability plan with:
+
+- capability summary
+- explicit non-goals
+- actors and surfaces
+- required states and transitions
+- interfaces / inputs / outputs
+- data model implications
+- security / billing / policy constraints
+- observability and operator requirements
+- open questions blocking implementation
+
+### 4. Translate into execution
+
+End with the exact handoff:
+
+- ready for direct implementation
+- needs architecture review first
+- needs product clarification first
+
+If useful, point to the next ECC-native lane:
+
+- `project-flow-ops`
+- `workspace-surface-audit`
+- `api-connector-builder`
+- `dashboard-builder`
+- `tdd-workflow`
+- `verification-loop`
+
+## Output Format
+
+Return the result in this order:
+
+```text
+CAPABILITY
+- one-paragraph restatement
+
+CONSTRAINTS
+- fixed rules, invariants, and boundaries
+
+IMPLEMENTATION CONTRACT
+- actors
+- surfaces
+- states and transitions
+- interface/data implications
+
+NON-GOALS
+- what this lane explicitly does not own
+
+OPEN QUESTIONS
+- blockers or product decisions still required
+
+HANDOFF
+- what should happen next and which ECC lane should take it
+```
+
+## Good Outcomes
+
+- Product intent is now concrete enough to implement without rediscovering hidden constraints mid-PR.
+- Engineering review has a durable artifact instead of relying on memory or Slack context.
+- The resulting plan is reusable across Claude Code, Codex, Cursor, OpenCode, and ECC 2.0 planning surfaces.