Scope committee_member.sfid forward mapping key by committee

The v2->v1 create path keyed the forward mapping on the v1 API
MemberID (contact SFID) alone, which the same contact reuses across
every committee it belongs to. Adding that contact to a second
committee silently overwrote the first committee's forward mapping,
orphaning it so a later v1-WAL delete couldn't find it. Scope the
create-path key by committee SFID and update the delete path to look
up the scoped key. Add a one-shot backfill to migrate existing flat
keys to the scoped format and tombstone stale entries whose committee
can no longer be resolved.

Issue: LFXV2-2709

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Signed-off-by: Jordan Evans <jevans@linuxfoundation.org>

Author: jordane

README.md

@@ -84,7 +84,8 @@ The following table shows the supported mapping key patterns and their expected
 | v1→v2 | `committee.sfid.{v1_sfid}` | `committee.sfid.123e4567-e89b-12d3-a456-426614174003` | `{v2_uuid}` | Committee SFID to UUID |
 | v2→v1 | `committee.uid.{v2_uuid}` | `committee.uid.123e4567-e89b-12d3-a456-426614174001` | `{project_sfid}:{committee_sfid}` | Committee UUID to compound SFID |
 | **Committee Members** |
-| v1→v2 | `committee_member.sfid.{v1_sfid}` | `committee_member.sfid.123e4567-e89b-12d3-a456-426614174004` | `{committee_uuid}:{member_uuid}` | Member SFID to compound UUID |
+| v1→v2 | `committee_member.sfid.{v1_sfid}` | `committee_member.sfid.123e4567-e89b-12d3-a456-426614174004` | `{committee_uuid}:{member_uuid}` | Member record SFID to compound UUID |
+| v1→v2 | `committee_member.sfid.{committee_sfid}.{member_sfid}` | `committee_member.sfid.a0941000002wBjEAAU.0034100000abcDEAAY` | `{committee_uuid}:{member_uuid}` | Member SFID to compound UUID, scoped by committee since the v1 API MemberID (contact SFID) is reused across committees for the same contact (LFXV2-2709) |
 | v2→v1 | `committee_member.uid.{v2_member_uuid}` | `committee_member.uid.123e4567-e89b-12d3-a456-426614174002` | `{project_sfid}:{committee_sfid}:{member_sfid}` | Member UUID to compound SFID |
 
 ### User SFID Lookup API
@@ -194,6 +195,47 @@ Locally (with NATS port-forwarded):
 lfx-v1-sync-helper --backfill-committee-member-mappings [--dry-run]
 ```
 
+**Committee-member forward-mapping migration (`--backfill-committee-member-forward-mappings`):**
+
+Migrates committee-member forward mappings written by the v2→v1 create path
+(`committee_member.sfid.{v1_sfid}`, keyed only on the contact SFID) to the committee-scoped
+format `committee_member.sfid.{committee_sfid}.{member_sfid}` — the fix for LFXV2-2709, where an
+unscoped key let MemberID reuse across committees silently overwrite an earlier committee's
+mapping. Skips v1-ingest forward keys (record sfid, a UUID) untouched. Because the collision
+already collapsed colliding committees' entries into a single flat key before this fix shipped,
+only the surviving (last-write) entry per contact can be migrated — this is cleanup, not data
+recovery. Writes are optimistic-concurrency guarded against the live sync-helper, idempotent, and
+safe to re-run.
+
+**Rollout note:** with the default single-replica `RollingUpdate` deployment, a new pod (writing
+the committee-scoped key) can briefly run alongside an old pod (whose delete handling only
+checks the pre-fix flat key), which can orphan a scoped mapping that this backfill's flat-key
+scan can't find. Deploy this release with `kubectl rollout restart` preceded by scaling to 0
+replicas (or equivalent `maxUnavailable: 0` / `maxSurge: 0` old→new cutover) rather than a
+default rolling update, to avoid old and new pods processing events concurrently.
+
+Run once after deploying the fix, to migrate already-affected mappings. A dry-run pass is
+recommended first:
+
+```sh
+kubectl --context lfx-v2-prod -n v1-sync-helper apply -f manifests/backfill-committee-member-forward-mappings-job.yaml
+```
+
+Add `--dry-run` to the manifest args, apply, inspect logs
+(`inspected`/`migrated`/`skipped_record_key`/`malformed`/`tombstoned`/`unresolved`/`conflicted`
+counts). A Job's pod template is immutable, so delete the dry-run Job before removing
+`--dry-run` and re-applying for the live run:
+
+```sh
+kubectl --context lfx-v2-prod -n v1-sync-helper delete job backfill-committee-member-forward-mappings
+```
+
+Locally (with NATS port-forwarded):
+
+```sh
+lfx-v1-sync-helper --backfill-committee-member-forward-mappings [--dry-run]
+```
+
 ## Architecture Diagrams
 
 Regarding the following sequence diagrams: