Avoid repeated prefix scans when projecting item policies

docs/roadmap/remediation.md

@@ -1,7 +1,7 @@
 # Sequence Implementation Review Remediation
 
-Status: remediation in progress. Completed findings are marked below; this
-record introduces no new release gate.
+Status: all eleven findings complete. Each finding has a separate remediation
+commit and completion note below. This record introduces no new release gate.
 
 Reviewed commit: `0be7cdb00eff576fda6b30c0600b2134d4e2e086`.
 Implementation range: `bc6b977..0be7cdb`.
@@ -25,6 +25,10 @@ Validation on the reviewed commit:
 - Finding 10 follows directly from the maintained text; finding 11 follows from
   the prefix-scan loop, not a timing comparison or performance threshold.
 
+Final validation after remediation: `./scripts/check.sh` and
+`go test -race ./...` passed with Go 1.26.10 on Linux. The original public-API
+probes for findings 1–9 now demonstrate the required corrected behavior.
+
 P1 denotes the highest-priority correctness issue here; P2 denotes normal-priority
 work needed to complete the selected behavior. Preserve the agreed scope while
 fixing these issues. In particular, do not resolve failures by restricting valid
@@ -376,7 +380,16 @@ Keep YAML-only enforcement distinct from registered final validation.
 
 ## 11. Remove The Quadratic Prefix Scan In Item Policy Projection — P2
 
-Status: [ ] Open.
+Status: [x] Complete.
+
+Completion: assigned sequence ranges now supply item offsets directly. Handoffs
+without a range lazily accumulate prefix lengths, visiting each preceding
+contribution once rather than rescanning every prefix. Regression coverage keeps
+inline and policy-less contributions in the correct positions with complete,
+partial, or absent ranges. Existing ownership/placement tests remain intact.
+Verified focused item-policy tests, `./scripts/check.sh`, `go test -race ./...`,
+and inspection of the remaining error-only prefix-scan callers. No new benchmark
+fixture or performance threshold was needed for this bounded change.
 
 Owner: [`projectNestedCollectionPolicies`](../../internal/engine/imports.go),
 especially line 968; the scanned helper is `priorSequenceLength` in the same file.