diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index e71670d..2fa58f6 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -246,3 +246,10 @@ jobs:
       - uses: actions/checkout@v7
       - name: Check version consistency
         run: ./scripts/check-version.sh
+  planning-hygiene:
+    name: Planning Hygiene
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v7
+      - name: Check no tracked planning-plane references
+        run: bash scripts/check-planning-hygiene.sh
diff --git a/.gitignore b/.gitignore
index 2f2d7eb..7f6d7b1 100644
--- a/.gitignore
+++ b/.gitignore
@@ -14,10 +14,11 @@ target/
 # Cargo.lock
 
 # -----------------------------------------------------------------------------
-# Planning and Local Configuration (NEVER COMMIT)
+# Planning and Local Configuration (kept out of the tree)
 # -----------------------------------------------------------------------------
-# Session planning documents - always local, never committed
-.plans/
+# Session planning documents are kept out of the working tree on purpose; this
+# entry is a convenience filter, not a security boundary.
+/.plans/
 
 # Local agent instructions - per-session tactical guidance
 AGENTS.local.md
diff --git a/.goneat/assess.yaml b/.goneat/assess.yaml
index 67ea705..a0e2d96 100644
--- a/.goneat/assess.yaml
+++ b/.goneat/assess.yaml
@@ -56,7 +56,6 @@ lint:
     ignore:
       - "**/target/**"
       - "**/.git/**"
-      - ".plans/**"
   # GitHub Actions linting
   github_actions:
     actionlint:
diff --git a/AGENTS.md b/AGENTS.md
index 7bab00e..4cc30c8 100644
--- a/AGENTS.md
+++ b/AGENTS.md
@@ -2,7 +2,7 @@
 
 ## Read First
 
-1. Check `AGENTS.local.md` if it exists (gitignored, tactical session guidance)
+1. **Check for local guidance** if present (e.g. `AGENTS.local.md`) — machine-specific instructions and tactical session overrides. Local context is kept out of the working tree on purpose; a `.gitignore` entry is a convenience filter, not a security boundary.
 2. Read `MAINTAINERS.md` for contacts and governance
 3. Review this document for operational protocols
 4. Understand: this is a **Rust library with cross-language bindings** — correctness is paramount
@@ -156,8 +156,8 @@ FFI boundary changes require extra scrutiny:
 - Change FFI contracts without review
 - Use `unsafe` without clear justification and review
 - Assume platform behavior without testing
-- **EVER commit anything from `.plans/`** - this directory is gitignored and MUST stay local
-- Commit `AGENTS.local.md` (gitignored - session-specific guidance)
+- **Add local planning paths, board names, or planning IDs to tracked content** — planning artifacts live in a private, maintainer-managed system kept outside the repository tree; a `.gitignore` entry is a convenience filter, not a security boundary
+- Commit `AGENTS.local.md` or other local guidance — it is kept out of the tree as defense-in-depth, not because a `.gitignore` entry makes it safe
 
 ## Critical Rules
 
@@ -281,6 +281,15 @@ FFI Architect — Bindings design and cross-language integration.
 - **FulmenHQ patterns**: https://github.com/fulmenhq/crucible
 - **Local decisions**: `docs/decisions/` (ADR, DDR, SDR)
 
+## Planning Artifacts
+
+- Feature briefs, task boards, and operational notes live in a private,
+  maintainer-managed planning system kept **outside** this repository tree —
+  not in-tree behind `.gitignore`, which is a convenience filter, not a security
+  boundary. This conforms to the [3 Leaps OSS Sensitive Local Data Policy](https://github.com/3leaps/oss-policies/blob/main/SENSITIVE-LOCAL-DATA.md).
+- Do not add local planning paths, board names, or planning IDs to tracked repo
+  content (code, docs, comments, commit messages, PR text).
+
 ## Contact
 
 - **Lead maintainer**: See MAINTAINERS.md
diff --git a/scripts/check-planning-hygiene.sh b/scripts/check-planning-hygiene.sh
new file mode 100755
index 0000000..06a50c7
--- /dev/null
+++ b/scripts/check-planning-hygiene.sh
@@ -0,0 +1,49 @@
+#!/usr/bin/env bash
+#
+# Planning-reference hygiene guard.
+#
+# Planning artifacts (briefs, task boards, IDs, memos) live in a private,
+# maintainer-managed system OUTSIDE this repository tree — see AGENTS.md →
+# "Planning Artifacts". A `.gitignore` entry is a convenience filter, not a
+# security boundary, so this guard asserts that no *tracked* file reintroduces
+# a reference to the private planning plane.
+#
+# This file stays self-sterile: the guarded tokens are spelled with character
+# classes ([.], [/], [-]) so the script never reintroduces the very substrings
+# it guards. The single permitted tracked reference is the anchored ignore
+# entry (an exact allowlist below), which names the retired directory as
+# defense-in-depth; every other guarded hit must fail.
+set -euo pipefail
+
+pattern='[.]plans|planning[/]|brief[-]ipcp|IPCP[-]TASK|IPCP[-][0-9]'
+permitted='^\.gitignore:[0-9]+:/[.]plans/$'
+
+# Content: allow only the single anchored ignore entry; reject every other
+# guarded hit in any tracked file.
+hits="$(git grep -nE "$pattern" || true)"
+if [ -n "$hits" ]; then
+	bad="$(printf '%s\n' "$hits" | grep -vE "$permitted" || true)"
+	if [ -n "$bad" ]; then
+		printf '%s\n' "$bad"
+		echo "::error::A tracked file references the private planning plane. Keep" \
+			"planning artifacts out of the repository tree (see AGENTS.md →" \
+			"Planning Artifacts)."
+		exit 1
+	fi
+fi
+perm_count="$(printf '%s\n' "$hits" | grep -cE "$permitted" || true)"
+if [ "$perm_count" -ne 1 ]; then
+	echo "::error::Expected exactly one permitted ignore entry, found $perm_count."
+	exit 1
+fi
+
+# Paths: no tracked path may reintroduce a planning-plane directory segment
+# (a content grep alone cannot see a sterile file added under a leaky path).
+tracked_paths="$(git ls-files | grep -E "$pattern" || true)"
+if [ -n "$tracked_paths" ]; then
+	printf '%s\n' "$tracked_paths"
+	echo "::error::A tracked file path references the private planning plane."
+	exit 1
+fi
+
+echo "OK: no private planning-plane references in tracked files."