Canonize work-record flavor and residual default-exclusion.

STATE-WP-0092-T01: flavor is a closed bucket on workplans and tasks;
residuals are a flavor, not a kind, and are omitted from default open
views until demand or risk promotes them. depends_on is the workplan
frontmatter edge.

.claude/rules/workplan-convention.md

@@ -11,6 +11,18 @@ Use `proposed` for a newly drafted plan, `ready` after review against current
 repo state, and `finished` when implementation is complete. `stalled` and
 `needs_review` are derived health labels, not stored statuses.
 
+Optional frontmatter (STATE-WP-0092):
+
+```yaml
+flavor: planning | implementation | refactoring | extension | residual
+depends_on:
+  - STATE-WP-0092
+```
+
+Unset `flavor` is not residual. Do not implement `flavor: residual` unless
+demand or risk has promoted it to another flavor. `depends_on` lists
+blocker **workplan** ids; that is the field C-20 indexes.
+
 Closed workplans may be moved to `workplans/archived/` with a completion-date
 prefix: `YYMMDD-CUST-WP-NNNN-<slug>.md`. The frontmatter id remains
 unchanged; the prefix is only for quick visual reference.