diff --git a/AGENTS.md b/AGENTS.md
index dc16122..9e76c53 100644
--- a/AGENTS.md
+++ b/AGENTS.md
@@ -33,6 +33,16 @@ close the pull request as merged by that commit. This exception changes only who
 creates the reviewed commit; it does not waive the branch, CI, review, or
 clean-head gates.
 
+## Protected master
+
+GitHub branch protection requires a pull request, an up-to-date passing
+`portable` check, resolved conversations, and linear history on `master`.
+Force pushes and deletion are disabled. Administrator enforcement remains off
+only so the privacy-safe local squash procedure above can preserve the required
+noreply identity. Use that bypass solely after all branch, local CI, hosted CI,
+remote-diff review, feedback, and clean-head gates pass; never use it for an
+ordinary direct implementation push.
+
 ## Milestone delivery loop
 
 For every roadmap increment:
diff --git a/CONTRIBUTING.md b/CONTRIBUTING.md
index e2a1574..556bdb0 100644
--- a/CONTRIBUTING.md
+++ b/CONTRIBUTING.md
@@ -7,10 +7,18 @@ Telosieve welcomes narrowly scoped research, security, documentation, integratio
 1. Start from current `master` with a clean worktree.
 2. Create a focused branch and state atomic acceptance criteria.
 3. Update implementation, behavioral tests, evidence, documentation, risks, compatibility, and roadmap state together.
-4. Run `./scripts/ci-local.sh`. While the repository is private, this is the sole authoritative CI gate; absent hosted checks are policy-compliant and must not be described as passing.
+4. Run `./scripts/ci-local.sh`; the complete local gate and applicable hosted
+   `portable` check must both pass.
 5. Open a pull request describing impact, validation, limitations, and any unresolved evidence gap.
 6. Address material review findings and rerun the complete local gate at the reviewed head.
 
+The protected `master` branch requires an up-to-date passing `portable` check,
+a pull request, resolved review conversations, and linear history. Force pushes
+and branch deletion are disabled. Repository-administrator bypass exists only
+for the documented privacy-safe local squash procedure in
+[Release Strategy](docs/RELEASE.md); it does not authorize ordinary direct
+pushes or omitted review.
+
 Do not add hosted CI, publish packages, change repository visibility, weaken fail-closed behavior, introduce mutation credentials, or broaden product claims without the separately documented approval gates.
 
 ## Engineering expectations
diff --git a/docs/IMPLEMENTATION_PLAN.md b/docs/IMPLEMENTATION_PLAN.md
index 3e1a866..ea7300b 100644
--- a/docs/IMPLEMENTATION_PLAN.md
+++ b/docs/IMPLEMENTATION_PLAN.md
@@ -1179,3 +1179,16 @@ Evidence: [Public Opening Decision](PUBLIC_OPENING_DECISION.md),
 [Release Strategy](RELEASE.md), [GitHub Pages Website](GITHUB_PAGES.md),
 `.github/workflows/`, `scripts/validate-hosted-workflows.py`, `CHANGELOG.md`, and
 `RELEASE_NOTES_v0.2.0-rc.4.md`.
+
+## Post-M68 - protected default branch
+
+- [x] Protect `master` with mandatory pull requests, strict up-to-date portable
+  CI, resolved conversations, linear history, and stale-approval dismissal.
+- [x] Disable force pushes and branch deletion.
+- [x] Retain administrator bypass only for the documented privacy-safe local
+  squash path, without weakening branch, CI, review, or clean-head gates.
+- [x] Verify the effective protection through the GitHub branch-protection API
+  and record the contributor and release procedure.
+
+Evidence: [Release Strategy](RELEASE.md), `AGENTS.md`, `CONTRIBUTING.md`, and
+GitHub branch protection for `master`.
diff --git a/docs/RELEASE.md b/docs/RELEASE.md
index d1471fa..3571d6e 100644
--- a/docs/RELEASE.md
+++ b/docs/RELEASE.md
@@ -226,6 +226,26 @@ public-history, Pages, and supply-chain checks on pull requests and
 and reproducible-build qualifications. Release requires both applicable hosted
 checks and a successful clean-head local gate.
 
+### Protected `master`
+
+GitHub branch protection on `master` requires:
+
+- a pull request, with stale approvals dismissed;
+- the strict, up-to-date `portable` GitHub Actions check;
+- resolved review conversations and linear history; and
+- force-push and branch-deletion prevention.
+
+The required approval count is zero because this owner-operated research
+repository does not yet have an independent maintainer quorum. This does not
+remove the pull-request or complete remote-diff review requirement.
+
+Administrator enforcement is deliberately disabled only for the narrow
+privacy-safe merge procedure in `AGENTS.md`: after the reviewed feature head
+passes local and hosted CI, the owner may create the squash commit locally with
+the repository noreply identity and push that reviewed commit to `master`.
+Using the bypass for unreviewed implementation, failed CI, force-pushing,
+deletion, or omitted pull-request evidence is prohibited.
+
 The bundle-signature protocol authenticates exact candidate bytes against a
 separately supplied context, time, signer, key identifier, and public key. Test
 keys are ephemeral. Promotion still requires approved operational signing