fix: address 4 unresolved PR review comments (round 2)

- Fix report sequence to use next available number (-002, -003, etc.)
  instead of hardcoded -002
- Use timestamped path when preserving prototype and directory already
  exists to prevent overwriting earlier preserved work
- Pass constraints summary in handoff to /ce:plan since plan skill
  does not auto-discover validation reports
- Add ce:prototype to README workflow table

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: rodrigohaertel-ctrl

plugins/compound-engineering/README.md

@@ -19,6 +19,7 @@ The primary entry points for engineering work, invoked as slash commands:
 |-------|-------------|
 | `/ce:ideate` | Discover high-impact project improvements through divergent ideation and adversarial filtering |
 | `/ce:brainstorm` | Explore requirements and approaches before planning |
+| `/ce:prototype` | Build throwaway prototypes to validate assumptions before planning |
 | `/ce:plan` | Create structured plans for any multi-step task -- software features, research workflows, events, study plans -- with automatic confidence checking |
 | `/ce:review` | Structured code review with tiered persona agents, confidence gating, and dedup pipeline |
 | `/ce:work` | Execute work items systematically |

plugins/compound-engineering/skills/ce-prototype/SKILL.md

@@ -171,7 +171,7 @@ For each goal, record:
 
 Read `assets/validation-report-template.md` for the report structure.
 
-Write the report to `docs/prototypes/<topic-slug>-validation-<date>.md`. If a report with the same name already exists (e.g., a second prototype round on the same day), append a sequence number: `<topic-slug>-validation-<date>-002.md`.
+Write the report to `docs/prototypes/<topic-slug>-validation-<date>.md`. If a report with the same name already exists (e.g., multiple prototype rounds on the same day), append the next available sequence number: `-002`, `-003`, etc.
 
 Create `docs/prototypes/` if it does not exist.
 
@@ -194,7 +194,7 @@ If anything is found, flag it to the user with a brief explanation. Let them dec
 
 Delete the prototype directory under `.context/compound-engineering/ce-prototype/`. The validation report in `docs/prototypes/` persists.
 
-If the user explicitly asks to keep the prototype, move it out of `.context/` (which is ephemeral scratch space subject to cleanup) to a durable location: `prototypes/<topic-slug>/` at the repo root. Note the preserved path in the validation report.
+If the user explicitly asks to keep the prototype, move it out of `.context/` (which is ephemeral scratch space subject to cleanup) to a durable location at the repo root: `prototypes/<topic-slug>/`. If that directory already exists (from a prior preserved prototype), use a timestamped path (`prototypes/<topic-slug>-<YYYYMMDD-HHMMSS>/`) to avoid overwriting earlier work. Note the preserved path in the validation report.
 
 #### 4.3 Recommend Next Step
 
@@ -209,7 +209,7 @@ Based on the validation results, recommend the appropriate next step:
 
 Present as a question using the platform's blocking question tool.
 
-**Handoff to /ce:plan:** When the user selects planning, run `/ce:plan` and pass the validation report path (e.g., `/ce:plan docs/prototypes/<topic-slug>-validation-<date>.md`). If a requirements document also exists, pass both paths. This ensures the plan has direct access to validated constraints and discovered surprises without relying on context window or user re-entry.
+**Handoff to /ce:plan:** When the user selects planning, run `/ce:plan` and pass both the requirements document path (if one exists) and a concise constraints summary extracted from the validation report. The summary should include: proved/disproved goal results, key constraints discovered, and the validation report path for reference. Example: `/ce:plan docs/brainstorms/2026-04-01-topic-requirements.md — Prototype validated: [goals summary]. Constraints: [key constraints]. Full report: docs/prototypes/topic-validation-2026-04-04.md`. This ensures planning starts from validated assumptions even if `/ce:plan` does not auto-discover validation reports.
 
 ### Phase 5 (Optional): Brainstorm Integration Suggestion
 

plugins/compound-engineering/skills/ce-prototype/references/validation-report-schema.md

@@ -37,7 +37,7 @@ Canonical frontmatter fields for prototype validation reports in `docs/prototype
 
 File: `docs/prototypes/<topic-slug>-validation-<YYYY-MM-DD>.md`
 
-If a report with the same name already exists (e.g., a second prototype round on the same day), append a sequence number: `<topic-slug>-validation-<YYYY-MM-DD>-002.md`.
+If a report with the same name already exists (e.g., multiple prototype rounds on the same day), append the next available sequence number: `-002`, `-003`, etc.
 
 Examples:
 - `docs/prototypes/stripe-refund-webhooks-validation-2026-04-04.md`