docs(canon): ADR-007 migration ruled — option 2, live renumber list empty

Verified: all five duplicated identifiers are finished, and no workplan in a
live state shares an identifier. Option 2 therefore requires no renumbering
today; historical duplicates stay, RAILIANCE-WP-0015 ambiguity included.

Separates remediation from conformance: three shared prefixes remain in use
across seven repos as single concurrently-allocated number lines. RAIL-BS-
and RAILIANCE- are still growing, so the 0015/0016 collisions will recur at
the next concurrent allocation. Prefix ownership assignment tracked as
RMGR-WP-0004-T09 under decision 1, which option 2 does not exempt.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

canon/architecture/adr-007-workplan-identity-and-repo-worker-topology.md

@@ -188,13 +188,62 @@ in increasing cost:
    `railiance-bootstrap`/`railiance-cluster` and `state-hub`'s legacy `CUST-WP-`
    files. Touches six repositories and every inbound reference.
 
-Recommendation: **option 2**, with option 3's prefix split applied only to repos
-that are still creating new workplans under a shared prefix — a shared prefix
-that is still growing keeps generating new collisions, while a dormant one does
-not.
+**Ruled 2026-08-17: option 2.** Renumber live collisions; leave
+`finished`/`archived` duplicates as historical record.
 
-All five duplicated identifiers are currently `finished`, so no active work is
-blocked by deferring this.
+### The live renumber list is empty
+
+Verified against the fleet scan. All five duplicated identifiers are `finished`:
+
+```text
+CUST-WP-0000       the-custodian ×2      finished
+CUST-WP-0010       the-custodian ×2      finished
+CUST-WP-0045       the-custodian ×2      finished
+RAILIANCE-WP-0015  apps, platform        finished
+RAILIANCE-WP-0016  apps, platform ×2     finished
+```
+
+No workplan in a `proposed`, `ready`, `active`, `blocked`, or `backlog` state
+shares an identifier with another. **Option 2 therefore requires no renumbering
+today.** Historical duplicates stay, including the `RAILIANCE-WP-0015` ambiguity
+between `railiance-apps` and `railiance-platform`; citations of it must name the
+repository.
+
+### The structural cause is not historical
+
+Option 2 governs *remediation*. It does not exempt anything from decision 1,
+which is accepted canon: one prefix, one repository, forward-only numbering.
+
+Three shared prefixes are still in use across seven repositories, and each is a
+**single number line being allocated from concurrently**:
+
+```text
+RAIL-BS-WP-    bootstrap  8, 9
+               cluster    7, 10, 11, 12, 13, 14
+
+RAILIANCE-WP-  platform   5, 8-17 (16 twice — an internal duplicate)
+               apps       15, 16          <- already collided with platform
+               forge      2
+               telemetry  1
+
+CUST-WP-       the-custodian  50 plans
+               state-hub       4 legacy plans (canonical prefix is STATE-WP)
+```
+
+`RAIL-BS-` and `RAILIANCE-` are actively growing — `RAIL-BS-WP-0014` (`ready`),
+`RAILIANCE-WP-0002` (`ready`), `RAILIANCE-WP-0001` (`proposed`), all created
+2026-08-11 or later. The `RAILIANCE-WP-0015`/`0016` collisions were not a
+historical accident; they are what concurrent allocation from a shared sequence
+produces, and it will recur at the next concurrent allocation.
+
+`CUST-` is dormant on the `state-hub` side — four legacy plans, one in
+`backlog` — and needs no split, only a prefix-ownership assertion.
+
+**Consequence.** Prefix ownership must be assigned for all three shared prefixes
+before the next workplan is created in the affected repositories. This is
+forward conformance under decision 1, not migration, and is tracked as
+`RMGR-WP-0004-T09`. Renaming the *historical* files is explicitly not required —
+that would be option 3, which was rejected.
 
 ## References