diff --git a/CHANGELOG.md b/CHANGELOG.md
index 29a1a88eec..398bac05a2 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -162,6 +162,10 @@
 
 ## Proposed
 
+- Compare GitHub repository identities case-insensitively at owned-head and
+  compare-ref boundaries so canonical casing drift cannot misroute an
+  organization-owned branch through external-fork restrictions.
+
 - Re-fetch authoritative open/Draft state and exact head immediately before
   both direct-merge and auto-merge mutations. A caller's stale Ready snapshot,
   a closed or unavailable PR, or a moved head now fails closed before any
diff --git a/docs/doctoring/case-insensitive-owned-head-identity.md b/docs/doctoring/case-insensitive-owned-head-identity.md
new file mode 100644
index 0000000000..e6b04cf7ae
--- /dev/null
+++ b/docs/doctoring/case-insensitive-owned-head-identity.md
@@ -0,0 +1,33 @@
+# Case-insensitive owned-head identity
+
+Decision date: **2026-09-07**
+
+## Problem
+
+GitHub treats repository names case-insensitively, but the scheduler compared
+`headRepository.nameWithOwner` with the configured target using exact string
+equality. Casing drift could classify an organization-owned branch as an
+external fork and build the wrong compare ref.
+
+## Decision
+
+Case-fold both repository identifiers in `same_repository_head` and
+`compare_ref_for_pr_head`. No permission or ownership inference changes; only
+names GitHub already considers identical are unified.
+
+## Failure scenes
+
+- `Owner/Repo` versus `owner/repo`: classify as the same repository.
+- A genuinely different repository: retain external-head handling.
+- Missing head repository metadata: preserve the existing compare fallback and
+  fail-closed mutation eligibility.
+
+## Evidence and follow-up
+
+RED commit: `4fb514db54e6210fc0606f0dfa8d9033f3e1f6f5`.
+Fresh exact-head hosted checks and independent review remain required.
+
+## Reference
+
+GitHub. (2026). *REST API endpoints for repositories*.
+https://docs.github.com/en/rest/repos/repos
diff --git a/docs/product-technical-gap-baseline.md b/docs/product-technical-gap-baseline.md
index 0d7db93ec6..a1642acfa6 100644
--- a/docs/product-technical-gap-baseline.md
+++ b/docs/product-technical-gap-baseline.md
@@ -3435,6 +3435,18 @@ same name in another file can carry the opposite safety property.**
 - **Evidence:** The original RED
   `2d140a84203a0df0cb86cd6b6ab31fc37bbdbda2` covered only an already-Draft
   caller. Corrective RED `897c7e6505a4c5dc203471109e425996f91fb9c9`
-  exercises both mutation entrypoints for a
-  same-head Ready→Draft race, moved head, missing live PR, and exact-ready
-  control. Fresh exact-head hosted checks remain required before integration.
+  exercises both mutation entrypoints for a same-head Ready→Draft race, moved
+  head, missing live PR, and exact-ready control. Fresh exact-head hosted
+  checks remain required before integration.
+
+
+### Case-insensitive owned-head identity
+
+- **Status:** Proposed
+- **Owner:** `ContextualWisdomLab/.github`
+- **Problem:** Same-repository head and compare-ref checks used case-sensitive
+  repository strings even though GitHub repository identity is case-insensitive.
+- **Action:** Case-fold both sides at the two owned-head routing boundaries.
+- **Evidence:** RED commit
+  `4fb514db54e6210fc0606f0dfa8d9033f3e1f6f5`; fresh exact-head hosted checks
+  remain required before integration.
diff --git a/scripts/ci/pr_review_merge_scheduler_core.py b/scripts/ci/pr_review_merge_scheduler_core.py
index 105428bdcb..76fabc7713 100644
--- a/scripts/ci/pr_review_merge_scheduler_core.py
+++ b/scripts/ci/pr_review_merge_scheduler_core.py
@@ -1552,7 +1552,7 @@ def compare_ref_for_pr_head(repo: str, pr: dict[str, Any]) -> str:
     """Return the compare-API head ref for a PR branch."""
     head_ref = pr.get("headRefName") or "HEAD"
     head_repo = (pr.get("headRepository") or {}).get("nameWithOwner")
-    if not head_repo or head_repo == repo:
+    if not head_repo or head_repo.casefold() == repo.casefold():
         return head_ref
     head_owner, _ = split_repo(head_repo)
     return f"{head_owner}:{head_ref}"
@@ -2988,7 +2988,7 @@ def post_update_branch_followup(
 def same_repository_head(repo: str, pr: dict[str, Any]) -> bool:
     """Return whether the PR head branch belongs to the repository being scanned."""
     head_repo = (pr.get("headRepository") or {}).get("nameWithOwner")
-    return head_repo == repo
+    return bool(head_repo) and head_repo.casefold() == repo.casefold()
 
 
 def can_update_pr_head(repo: str, pr: dict[str, Any]) -> bool:
diff --git a/tests/test_pr_review_merge_scheduler.py b/tests/test_pr_review_merge_scheduler.py
index 4568a020f1..7635647843 100644
--- a/tests/test_pr_review_merge_scheduler.py
+++ b/tests/test_pr_review_merge_scheduler.py
@@ -10900,6 +10900,15 @@ def test_draft_pr_cannot_reach_merge_mutations(monkeypatch):
     assert calls == []
 
 
+def test_same_repository_identity_is_case_insensitive():
+    """GitHub casing drift cannot route an owned branch through the fork path."""
+    pull_request = make_pr(
+        headRefName="feature",
+        headRepository={"nameWithOwner": "Owner/Repo"},
+    )
+
+    assert sched.same_repository_head("owner/repo", pull_request)
+    assert sched.compare_ref_for_pr_head("owner/repo", pull_request) == "feature"
 @pytest.mark.parametrize("mutation", (sched.enable_auto_merge, sched.merge_pr))
 def test_merge_mutation_rechecks_live_draft_state(monkeypatch, mutation):
     """A Ready snapshot cannot mutate after the live PR becomes Draft."""