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 ---
 
+## Shared conventions
+
+- [Canonical plan naming convention](docs/plan-naming-convention.md) — portable hierarchy and overflow rules for planning artifacts shared across repositories.
+
+---
+
 ## Requirements
 
 Required:
diff --git a/docs/plan-naming-convention.md b/docs/plan-naming-convention.md
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+# Canonical plan naming convention
+
+This document is the portable, versioned source of truth for naming planning artifacts across repositories.
+
+## Normative hierarchy
+
+```text
+Plan → Session → Module → Task
+```
+
+Spanish repositories use the equivalent labels:
+
+```text
+Plan → Sesión → Módulo → Tarea
+```
+
+- **Plan (`P<n>`)**: a durable product or technical outcome with its own identity.
+- **Session (`S<plan>.<n>`)**: the reviewable delivery boundary normally associated with one pull request.
+- **Module (`M<plan>.<session>.<n>`)**: files or concerns that must change together inside a Session.
+- **Task (`T<plan>.<session>.<module>.<n>`)**: an atomic, verifiable action.
+
+Time is an estimate (`est:`), never a hierarchy boundary. A Session is not defined as “1–3 hours” or as work completed in one sitting.
+
+## Overflow rule
+
+A Session should normally fit in one pull request. If its reviewed scope exceeds one PR, either:
+
+1. split the scope into multiple Sessions; or
+2. preserve the same Session and deliver its Modules through chained PRs.
+
+In the second case, every chained PR must name the parent Session and the Modules it delivers. The chain is delivery mechanics, not an additional planning level.
+
+## Reserved planning vocabulary
+
+Do not introduce `WU`, `Work Unit`, `phase`, `fase`, `slice`, `bloque`, `paquete`, `stage`, `milestone`, or `track` as planning levels.
+
+Valid exceptions:
+
+- `slice` may remain when it is an actual Control Tower domain entity or describes chained-PR mechanics;
+- `work unit` may remain when it describes mechanical grouping of commits;
+- schemas, IDs, fields, routes, filenames, product entities, and immutable historical evidence are not renamed merely because they contain one of these words.
+
+Historical documents may retain legacy vocabulary only when they are clearly marked **ARCHIVED / NON-ACTIONABLE** and do not act as current planning authority. Active documents must use the canonical hierarchy.
+
+## Portable references
+
+Repositories should link to this versioned document rather than relying on machine-specific paths such as `/home/<user>/...` or `~/.claude/...` as their only source.