feat(skill): introduce CONCEPTS.md as shared vocabulary substrate

plugins/compound-engineering/AGENTS.md

@@ -12,7 +12,7 @@ They supplement the repo-root `AGENTS.md`.
 Consequences:
 
 - Behavioral rules that govern skill *runtime* behavior must live inside the skill itself — in `SKILL.md` or files under its `references/`. Guidance placed in this file is invisible at runtime.
-- When two or more skills share a behavioral principle, duplicate the guidance into each skill (inline for short rules, `references/` for longer ones). There is no cross-skill shared-file mechanism (see "File References in Skills" below).
+- When two or more skills share a behavioral principle, duplicate the guidance into each skill (inline for short rules, `references/` for longer ones). There is no cross-skill shared-file mechanism (see "File References in Skills" below). When a reference file is duplicated across skills (e.g., `concepts-vocabulary.md` in both `ce-compound/references/` and `ce-compound-refresh/references/`), edits must be applied to every copy in the same commit. Drift between copies produces inconsistent agent behavior depending on which skill loaded.
 - Do not propose that runtime guidance for ce-ideate, ce-brainstorm, ce-plan, or any other skill live in this AGENTS.md or in the repo-root AGENTS.md. Those files only shape how contributors edit the plugin.
 
 This is easy to miss because authoring feels like using: you edit the plugin while running inside this repo, and the repo's AGENTS.md is loaded — but that load does not follow the installed skill into a user's environment.

plugins/compound-engineering/agents/ce-learnings-researcher.md

@@ -18,6 +18,12 @@ Past learnings span multiple shapes:
 
 Treat all of these as candidates. Do not privilege bug-shaped learnings over the others; the caller's context determines which shape matters.
 
+## Step 0: Ground in CONCEPTS.md (if present)
+
+Before searching `docs/solutions/`, check whether `CONCEPTS.md` exists at the repo root. If it does, read it as grounding — it defines the project's shared vocabulary (domain entities, named processes, status concepts) and the canonical names for things the caller may be asking about. Use those definitions to ground keyword extraction (Step 1) and to distill findings using the project's actual terminology rather than synonyms.
+
+If `CONCEPTS.md` does not exist, skip this step entirely and proceed to Step 1.
+
 ## Search Strategy (Grep-First Filtering)
 
 The `docs/solutions/` directory contains documented learnings with YAML frontmatter. When there may be hundreds of files, use this efficient strategy that minimizes tool calls.

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

@@ -137,7 +137,7 @@ Scan the repo before substantive brainstorming. Match depth to scope:
 
 **Standard and Deep** — Two passes:
 
-*Constraint Check* — Check project instruction files (`AGENTS.md`, and `CLAUDE.md` only if retained as compatibility context) for workflow, product, or scope constraints that affect the brainstorm. Also read `STRATEGY.md` if it exists — the product's target problem, approach, persona, and active tracks are direct input to what this brainstorm should deliver and should shape scope, success criteria, and which approaches are aligned vs out-of-scope. If these add nothing, move on.
+*Constraint Check* — Check project instruction files (`AGENTS.md`, and `CLAUDE.md` only if retained as compatibility context) for workflow, product, or scope constraints that affect the brainstorm. Also read `STRATEGY.md` if it exists — the product's target problem, approach, persona, and active tracks are direct input to what this brainstorm should deliver and should shape scope, success criteria, and which approaches are aligned vs out-of-scope. Also read `CONCEPTS.md` at repo root if it exists — the project's authoritative vocabulary. Use these names in dialogue, approaches, and the requirements doc; map user-offered synonyms back. If any of these add nothing, move on.
 
 *Topic Scan* — Search for relevant terms. Read the most relevant existing artifact if one exists (brainstorm, plan, spec, skill, feature doc). Skim adjacent examples covering similar behavior.
 
@@ -210,6 +210,18 @@ Follow the Interaction Rules above. Use the platform's blocking question tool wh
 
 **Exit condition:** Continue until the idea is clear AND no integration-check questions are pending, OR the user explicitly wants to proceed.
 
+#### 1.4 Vocabulary Capture (only if CONCEPTS.md already exists)
+
+**Skip this sub-phase entirely if `CONCEPTS.md` does not exist at repo root** — creation is owned by ce-compound and ce-compound-refresh.
+
+If it exists, scan the dialogue for **resolved** domain terms — terms where the conversation actively pinned down a precise local meaning, not terms merely mentioned in passing. **Resolved means the dialogue is no longer questioning the definition.** Provisional terms that may still revise stay in the conversation only.
+
+For each resolved term: if missing, add it; if present but the dialogue surfaced new precision, refine it; if already consistent, no action.
+
+**Domain entities, named processes, and status concepts with project-specific meaning only.** Not file paths, class names, function signatures, or implementation decisions — `CONCEPTS.md` is a glossary, not a spec or catch-all.
+
+Follow the format set by existing entries. Apply edits silently.
+
 ### Phase 2: Explore Approaches
 
 If multiple plausible directions remain, propose **2-3 concrete approaches** based on research and conversation. Otherwise state the recommended direction directly.

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

@@ -165,6 +165,7 @@ A learning has several dimensions that can independently go stale. Surface-level
 - **Related docs** — are cross-referenced learnings and patterns still present and consistent?
 - **Auto memory** (Claude Code only) — does the injected auto-memory block in your system prompt contain entries in the same problem domain? Scan that block directly. If the block is absent, skip this dimension. A memory note describing a different approach than what the learning recommends is a supplementary drift signal.
 - **Overlap** — while investigating, note when another doc in scope covers the same problem domain, references the same files, or recommends a similar solution. For each overlap, record: the two file paths, which dimensions overlap (problem, solution, root cause, files, prevention), and which doc appears broader or more current. These signals feed Phase 1.75 (Document-Set Analysis).
+- **Vocabulary** — note domain terms the learning cites (entities, named processes, status concepts with project-specific meaning). For each term: does it appear in `CONCEPTS.md`? If yes, does the definition still match how the code uses the term? If no, flag the term for Phase 4.5 to add or bootstrap. Do not edit `CONCEPTS.md` during investigation — just collect the signal centrally.
 
 Match investigation depth to the learning's specificity — a learning referencing exact file paths and code snippets needs more verification than one describing a general principle.
 
@@ -486,6 +487,31 @@ For each candidate, execute the flow that matches its classification from Phase
 
 Only one flow runs per candidate; the reference contains the per-action criteria, examples, and step-by-step instructions.
 
+## Phase 4.5: Vocabulary Capture
+
+After the per-learning actions execute, aggregate the domain terms flagged across Phase 1's Vocabulary dimension and reconcile them with `CONCEPTS.md`.
+
+**First, read `references/concepts-vocabulary.md`.** This is unconditional. Do not pre-judge from memory which Phase 1 signals qualify — the reference's criteria are non-obvious and a "nothing qualifies" judgment without reading is a shortcut, not a result.
+
+**Procedure:**
+
+1. **Aggregate.** Collect qualifying terms surfaced across the learnings in scope, applying the reference's criteria. If the same term surfaced in multiple learnings with different shades of precision, **union the shades into one entry** — not three entries, not most-recent-wins.
+2. **If `CONCEPTS.md` exists**, add missing terms and refine existing entries when the corpus surfaced new precision. Do not duplicate entries already present.
+3. **If `CONCEPTS.md` does not exist** and at least one qualifying term was surfaced, **bootstrap it**. One term is enough — do not gate creation behind a minimum count, that creates an asymmetric trap where the file only ever gets created on the second eligible run. **At creation, hold the qualifying bar conservatively** — a borderline term or a class/table/file name dressed up as an entity should defer until a later run surfaces stronger signal. The conservatism is about quality, not count; updates to an existing file follow normal criteria.
+4. **Scope discipline and citation hygiene.** Bootstrap reflects only the area in scope — do not expand to other categories, and do not retroactively inject `(see CONCEPTS.md)` pointers into existing learnings. The report should note that additional entries are likely from refresh runs on other scopes.
+5. **Initial structure.** When bootstrapping, start the file with this preamble under the `# Concepts` heading:
+
+   > Shared domain vocabulary for this project — entities, named processes, and status concepts with project-specific meaning. Accretes as ce-compound and ce-compound-refresh process learnings; direct edits are fine. Glossary only, not a spec or catch-all.
+
+   Then add entries. Let term count drive shape: 1-4 terms → flat headings, more → cluster by domain relationship per the rules in `references/concepts-vocabulary.md`.
+6. **Scrub violations.** Scan existing entries for content that violates `references/concepts-vocabulary.md` criteria — implementation specifics (file paths, class names, function signatures, code references), status/owner/date metadata, or duplicates of terms covered under a different name. Rewrite or consolidate. The full sweep is appropriate here because refresh is an audit; ce-compound's same-named phase scopes corrections to entries already being touched.
+
+If no Phase 1 signals qualified after applying the reference's criteria, record that outcome explicitly in the report's `CONCEPTS.md` line (e.g., "scanned, no qualifying terms"). Do not silently skip — the visible scan-and-no-result record is the audit signal that the reference was consulted.
+
+Note: if this run **creates** `CONCEPTS.md` from scratch, the Discoverability Check below must also surface it in `AGENTS.md`/`CLAUDE.md` so future agents discover it. Subsequent runs skip this because the instruction file is already current.
+
+**Apply edits silently — no user prompt in any mode.** Vocabulary capture is a side effect of refreshing, not a decision the user makes per run.
+
 ## Output Format
 
 **The full report MUST be printed as markdown output.** Do not summarize findings internally and then output a one-liner. The report is the deliverable — print every section in full, formatted as readable markdown with headers, tables, and bullet points.
@@ -504,6 +530,8 @@ Replaced: Z
 Deleted: W
 Skipped: V
 Marked stale: S
+
+CONCEPTS.md: <scanned, no qualifying terms | created with N entries | updated — N added, N refined, N scrubbed>
 ```
 
 Then for EVERY file processed, list:
@@ -631,4 +659,12 @@ After the refresh report is generated, check whether the project's instruction f
       ```
    c. In interactive mode, explain to the user why this matters — agents working in this repo (including fresh sessions, other tools, or collaborators without the plugin) won't know to check `docs/solutions/` unless the instruction file surfaces it. Show the proposed change and where it would go, then use the platform's blocking question tool to get consent before making the edit: `AskUserQuestion` in Claude Code (call `ToolSearch` with `select:AskUserQuestion` first if its schema isn't loaded), `request_user_input` in Codex, `ask_user` in Gemini, `ask_user` in Pi (requires the `pi-ask-user` extension). Fall back to presenting the proposal in chat only when no blocking tool exists in the harness or the call errors (e.g., Codex edit modes) — not because a schema load is required. Never silently skip the question. In headless mode, include it as a "Discoverability recommendation" line in the report — do not attempt to edit instruction files (headless scope is doc maintenance, not project config).
 
-5. **Amend or create a follow-up commit when the check produces edits.** If step 4 resulted in an edit to an instruction file and Phase 5 already committed the refresh changes, stage the newly edited file and either amend the existing commit (if still on the same branch and no push has occurred) or create a small follow-up commit (e.g., `docs: add docs/solutions/ discoverability to AGENTS.md`). If Phase 5 already pushed the branch to a remote (e.g., the branch+PR path), push the follow-up commit as well so the open PR includes the discoverability change. This keeps the working tree clean and the remote in sync at the end of the run. If the user chose "Don't commit" in Phase 5, leave the instruction-file edit unstaged alongside the other uncommitted refresh changes — no separate commit logic needed.
+5. **If `CONCEPTS.md` exists at repo root, run a parallel discoverability check for it.** Use the same workflow as the `docs/solutions/` check above: same target file, same edit-placement judgment, same consent-then-edit interaction shape per mode. Example calibration when a directory listing is present:
+
+   ```
+   CONCEPTS.md  # shared domain vocabulary — read when orienting to the codebase or before discussing domain concepts
+   ```
+
+   **Skip this step entirely if `CONCEPTS.md` does not exist** — never nag for an artifact the project has not adopted. When skipped, this step produces no output and no edit.
+
+6. **Amend or create a follow-up commit when the check produces edits.** If step 4 or step 5 resulted in an edit to an instruction file and Phase 5 already committed the refresh changes, stage the newly edited file and either amend the existing commit (if still on the same branch and no push has occurred) or create a small follow-up commit (e.g., `docs: add docs/solutions/ discoverability to AGENTS.md`, or `docs: add CONCEPTS.md discoverability to AGENTS.md`, or a combined message when both edits landed). If Phase 5 already pushed the branch to a remote (e.g., the branch+PR path), push the follow-up commit as well so the open PR includes the discoverability change. This keeps the working tree clean and the remote in sync at the end of the run. If the user chose "Don't commit" in Phase 5, leave the instruction-file edits unstaged alongside the other uncommitted refresh changes — no separate commit logic needed.

plugins/compound-engineering/skills/ce-compound-refresh/references/concepts-vocabulary.md

@@ -0,0 +1,62 @@
+# CONCEPTS.md vocabulary rules
+
+`CONCEPTS.md` defines the words that mean something specific in this codebase — substrate that `docs/solutions/` and AGENTS.md can cite without redefinition. Lives at the repo root, created lazily the first time a learning surfaces a qualifying term.
+
+## Be opinionated
+
+When the team uses several words for the same concept, pick the best one and retire the rest. Record retired synonyms as aliases on the entry (see "Per entry"). Settled distinctions go to the Flagged ambiguities tail. The glossary is not a record of all words the team has ever used — it is the team's agreed-upon vocabulary.
+
+## The file stands on its own
+
+Each entry teaches its concept to a reader with no access to anything else — no codebase, no PR history, no architecture meetings, no Slack. This rules out:
+
+- Implementation specifics (file paths, class names, function signatures, table names, library calls)
+- Status fields, dates, owners on the entries
+- Examples drawn from current code
+- Links to PRs, issues, channels, or roadmap milestones
+- Version-specific claims ("currently uses X; migrating to Y")
+
+Cross-references between entries within `CONCEPTS.md` are fine — they resolve internally. General programming vocabulary (caches, queues, jobs, sessions) and everyday domain English need no redefinition either.
+
+## What earns a slot
+
+A term qualifies when its meaning here is precise enough that a new engineer would need it defined to follow conversations, tickets, or code. General programming vocabulary does not belong, even when used heavily.
+
+## Per entry
+
+Definition is one sentence — what the term means in this domain, what makes it distinct from neighbors. A term with non-obvious behavioral rules (lifecycle, cancellation semantics, ownership invariants) earns a second paragraph for those rules — never for elaborating the definition itself.
+
+When retired synonyms exist, list them as an aliases line directly under the definition: *Avoid: Booking, appointment*. Entities typically need more depth than value types; status concepts may need transition notes.
+
+## Relationships (optional)
+
+When relationships between entries carry load-bearing meaning (ownership, cardinality, lifecycle dependencies that span entries), capture them in a `## Relationships` section near the top of the file or its cluster. Skip when entries stand on their own without structural context — relationships are a lift for domains where structure is part of what makes terms meaningful, not a routine section.
+
+## Organization
+
+Cluster concepts by domain relationship — entities with their states, processes with their stages — so a reader sees structure without effort. A flat list works when the file is small. Reshape as the file grows.
+
+## Flagged ambiguities (tail of file)
+
+When two terms were used interchangeably and the team settled on a distinction, record the resolution as a one-line note: *"'account' had been used for both Customer and User — these are distinct."* This section is the audit trail for opinions the team has formed.
+
+## One illustrative entry — the shape, not a template
+
+```
+## Booking
+
+### Reservation
+A future commitment to seat a Party at a specified date and time.
+*Avoid:* Booking, appointment
+
+A Reservation owns its Party but does not own a Table — Tables are acquired only when the Party arrives, through a Seating. Lifecycle: Booked, Seated, Completed, No-Show. Cancellation before a Seating is non-destructive; cancellation after a Seating is recorded as a No-Show.
+
+### Party
+The guests committed to a Reservation. Each Reservation has exactly one Party. Party size is the count promised at booking, not the count who arrive.
+
+### Table
+A physical seating unit with fixed capacity. Tables are shared resources — they do not belong to Reservations and are allocated only on the day-of through Seatings.
+
+### Seating
+The act of placing a Party at a Table once the Party arrives. A Reservation has at most one Seating; a Table accumulates many Seatings across its lifetime.
+```