diff --git a/packages/mosaic/framework/tools/git/pr-edit.sh b/packages/mosaic/framework/tools/git/pr-edit.sh
index 47a12d8e..f5db9fb4 100755
--- a/packages/mosaic/framework/tools/git/pr-edit.sh
+++ b/packages/mosaic/framework/tools/git/pr-edit.sh
@@ -50,38 +50,45 @@ Options:
     -H, --host HOST        Explicit Gitea host (required with --repo off-host)
     -h, --help             Show this help message
 EOF
-    exit "${1:-1}"
+    exit "${1:-2}"
+}
+
+# Usage-error contract (R4, 2026-08-28): usage errors print to STDERR and exit 2,
+# distinct from provider, credential, and verification failures (exit 1).
+usage_error() {
+    echo "Error: $*" >&2
+    usage
 }
 
 while [[ $# -gt 0 ]]; do
     case "$1" in
-        -n|--number) PR_NUMBER="${2:-}"; shift 2 ;;
-        -t|--title) TITLE="${2:-}"; shift 2 ;;
-        -b|--body) BODY="${2:-}"; shift 2 ;;
-        -B|--base) BASE_BRANCH="${2:-}"; shift 2 ;;
+        -n|--number) [[ $# -ge 2 ]] || usage_error "option $1 requires a value"; PR_NUMBER="${2:-}"; shift 2 ;;
+        -t|--title) [[ $# -ge 2 ]] || usage_error "option $1 requires a value"; TITLE="${2:-}"; shift 2 ;;
+        -b|--body) [[ $# -ge 2 ]] || usage_error "option $1 requires a value"; BODY="${2:-}"; shift 2 ;;
+        -B|--base) [[ $# -ge 2 ]] || usage_error "option $1 requires a value"; BASE_BRANCH="${2:-}"; shift 2 ;;
         --draft)
-            [[ "$DRAFT_MODE" != "ready" ]] || { echo "Error: --draft and --ready are mutually exclusive" >&2; exit 1; }
+            [[ "$DRAFT_MODE" != "ready" ]] || { echo "Error: --draft and --ready are mutually exclusive" >&2; exit 2; }
             DRAFT_MODE="draft"; shift ;;
         --ready)
-            [[ "$DRAFT_MODE" != "draft" ]] || { echo "Error: --draft and --ready are mutually exclusive" >&2; exit 1; }
+            [[ "$DRAFT_MODE" != "draft" ]] || { echo "Error: --draft and --ready are mutually exclusive" >&2; exit 2; }
             DRAFT_MODE="ready"; shift ;;
-        -l|--login) LOGIN_OVERRIDE="${2:-}"; shift 2 ;;
-        -r|--repo) REPO_OVERRIDE="${2:-}"; shift 2 ;;
-        -H|--host) HOST_OVERRIDE="${2:-}"; shift 2 ;;
+        -l|--login) [[ $# -ge 2 ]] || usage_error "option $1 requires a value"; LOGIN_OVERRIDE="${2:-}"; shift 2 ;;
+        -r|--repo) [[ $# -ge 2 ]] || usage_error "option $1 requires a value"; REPO_OVERRIDE="${2:-}"; shift 2 ;;
+        -H|--host) [[ $# -ge 2 ]] || usage_error "option $1 requires a value"; HOST_OVERRIDE="${2:-}"; shift 2 ;;
         -h|--help) usage 0 ;;
         *) echo "Unknown option: $1" >&2; usage ;;
     esac
 done
 
-[[ -n "$PR_NUMBER" ]] || { echo "Error: Pull request number is required (-n)" >&2; exit 1; }
-[[ "$PR_NUMBER" =~ ^[1-9][0-9]*$ ]] || { echo "Error: Pull request number must be a positive integer" >&2; exit 1; }
+[[ -n "$PR_NUMBER" ]] || { echo "Error: Pull request number is required (-n)" >&2; exit 2; }
+[[ "$PR_NUMBER" =~ ^[1-9][0-9]*$ ]] || { echo "Error: Pull request number must be a positive integer" >&2; exit 2; }
 if [[ -z "$TITLE" && -z "$BODY" && -z "$BASE_BRANCH" && -z "$DRAFT_MODE" ]]; then
     echo "Error: At least one edit option is required" >&2
-    exit 1
+    exit 2
 fi
 [[ -z "$REPO_OVERRIDE" || "$REPO_OVERRIDE" =~ ^[^/[:space:]]+/[^/[:space:]]+$ ]] || {
     echo "Error: --repo must be OWNER/REPO" >&2
-    exit 1
+    exit 2
 }
 
 if [[ -n "$HOST_OVERRIDE" || -n "$REPO_OVERRIDE" ]]; then
@@ -92,7 +99,7 @@ fi
 
 case "$PLATFORM" in
     github)
-        [[ -z "$LOGIN_OVERRIDE" ]] || { echo "Error: --login is only valid for Gitea" >&2; exit 1; }
+        [[ -z "$LOGIN_OVERRIDE" ]] || { echo "Error: --login is only valid for Gitea" >&2; exit 2; }
         if [[ -n "$TITLE" || -n "$BODY" || -n "$BASE_BRANCH" ]]; then
             CMD=(gh pr edit "$PR_NUMBER")
             [[ -n "$TITLE" ]] && CMD+=(--title "$TITLE")
diff --git a/packages/mosaic/framework/tools/git/test-pr-edit-usage-contract.sh b/packages/mosaic/framework/tools/git/test-pr-edit-usage-contract.sh
new file mode 100755
index 00000000..e816f69d
--- /dev/null
+++ b/packages/mosaic/framework/tools/git/test-pr-edit-usage-contract.sh
@@ -0,0 +1,133 @@
+#!/usr/bin/env bash
+# Usage-error contract for pr-edit.sh (R4, 2026-08-28).
+#
+# issue-edit already uses long-flag-first parsing (-i/--issue, -t/--title,
+# -b/--body, -l/--labels, -m/--milestone); this adds the rc=2 usage-error
+# contract, value checks, and the no-provider-contact proof. Required: -i.
+#
+# Arms:
+#   1. --help and -h exit 0 and print usage.
+#   2. Unknown option exits 2 with the message on stderr.
+#   3. Missing required -i exits 2 (stderr).
+#   4. A value-less flag (-i -b -c and long forms) exits 2 (stderr).
+#   5. -b and -c both pass parsing (sandboxed runner: the run then fails
+#      at credential resolution, nonzero and NOT 2) — no real token is
+#      ever read and no provider is contacted.
+#   6. No arm performs any provider request (PATH shims record every
+#      invocation; the probe log must stay empty).
+set -euo pipefail
+
+SCRIPT_DIR="$(cd "$(dirname "${BASH_SOURCE[0]}")" && pwd)"
+WORK_DIR="${MOSAIC_TEST_WORK_DIR:-$PWD/.mosaic-test-work/pr-edit-usage}"
+BIN_DIR="$WORK_DIR/bin"
+PROBE_LOG="$WORK_DIR/provider-probes.log"
+OUT_FILE="$WORK_DIR/out.log"
+ERR_FILE="$WORK_DIR/err.log"
+
+cleanup() {
+    rm -rf "$WORK_DIR"
+}
+trap cleanup EXIT
+
+mkdir -p "$BIN_DIR"
+: > "$PROBE_LOG"
+
+# Unlike the issue suites, these stubs FAIL (exit 99): pr-close has an
+# API fallback that treats a successful curl as a closed PR, so exit-0
+# stubs would let the sandbox arms "succeed" (measured 2026-08-28).
+for tool in gh tea curl; do
+    cat > "$BIN_DIR/$tool" <<STUB
+#!/usr/bin/env bash
+echo "$tool \$*" >> "$PROBE_LOG"
+exit 99
+STUB
+    chmod +x "$BIN_DIR/$tool"
+done
+
+run_wrapper() {
+    ( cd "$WORK_DIR" && PATH="$BIN_DIR:$PATH" "$SCRIPT_DIR/pr-edit.sh" "$@" )
+}
+
+# Hermetic variant: neutralizes every identity/credential source the wrapper
+# consults so parse-acceptance arms fail at credential resolution in ANY cwd
+# repo (see test-issue-comment-usage-contract.sh for the measured incident).
+run_wrapper_sandboxed() {
+    mkdir -p "$WORK_DIR/home" "$WORK_DIR/xdg"
+    (
+        cd "$WORK_DIR"
+        PATH="$BIN_DIR:$PATH" HOME="$WORK_DIR/home" XDG_CONFIG_HOME="$WORK_DIR/xdg" \
+            MOSAIC_GIT_IDENTITY="" MOSAIC_BRAIN_HOME="" \
+            "$SCRIPT_DIR/pr-edit.sh" "$@"
+    )
+}
+
+fail() {
+    echo "FAIL: $*" >&2
+    echo "--- stderr ---" >&2
+    cat "$ERR_FILE" >&2
+    exit 1
+}
+
+expect_rc() { # expect_rc <want> <desc> <args...>
+    local want="$1" desc="$2" rc=0
+    shift 2
+    run_wrapper "$@" >"$OUT_FILE" 2>"$ERR_FILE" || rc=$?
+    [[ "$rc" -eq "$want" ]] || fail "$desc: rc=$rc, want $want"
+}
+
+expect_stderr() { # expect_stderr <pattern> <desc>
+    grep -q "$1" "$ERR_FILE" || fail "$2: stderr missing '$1'"
+}
+
+# 1. Help exits 0 and prints usage.
+expect_rc 0 "--help exits 0" --help
+grep -q "Usage: pr-edit.sh" "$OUT_FILE" || fail "--help did not print usage"
+expect_rc 0 "-h exits 0" -h
+
+# 2. Unknown option: rc 2, stderr.
+expect_rc 2 "unknown option exits 2" --bogus
+expect_stderr "[Uu]nknown option" "unknown option names itself on stderr"
+
+# 3. Missing required PR number: rc 2, stderr.
+expect_rc 2 "missing -n exits 2"
+expect_stderr "Pull request number is required" "missing -n message on stderr"
+expect_rc 2 "no edit option exits 2" -n 5
+expect_stderr "At least one edit option is required" "no-edit-option message on stderr"
+expect_rc 2 "non-integer PR number exits 2" -n abc -t x
+expect_stderr "positive integer" "integer check on stderr"
+expect_rc 2 "mutually exclusive draft/ready exits 2" -n 5 --draft --ready
+expect_stderr "mutually exclusive" "mutual exclusion on stderr"
+expect_rc 2 "bad repo format exits 2" -n 5 -t x -r not-a-slug
+expect_stderr "OWNER/REPO" "repo format on stderr"
+
+
+# 4. Value-less flags: rc 2 with "requires a value" on stderr.
+for flag in -n -t -b -B -l -r -H --number --title --body --base --login --repo --host; do
+    expect_rc 2 "value-less $flag exits 2" "$flag"
+    expect_stderr "requires a value" "value-less $flag message on stderr"
+done
+
+# 4b. Parser-failure arms (1-4) must have performed ZERO provider contact.
+if [[ -s "$PROBE_LOG" ]]; then
+    echo "FAIL: a parser-failure arm contacted a provider:" >&2
+    cat "$PROBE_LOG" >&2
+    exit 1
+fi
+
+# 5. Alias acceptance under the sandbox: both -b and -c carry a value past
+#    parsing; the run fails at credential resolution nonzero and NOT 2.
+for flag in -b; do
+    rc=0
+    run_wrapper_sandboxed -n 5 "$flag" "value" >"$OUT_FILE" 2>"$ERR_FILE" || rc=$?
+    [[ "$rc" -ne 0 ]] || fail "$flag arm unexpectedly succeeded in the sandbox"
+    [[ "$rc" -ne 2 ]] || fail "$flag arm misclassified credential failure as a usage error"
+done
+
+# 6. Post-sandbox provider assertions are intentionally NOT applied here:
+# pr-close's gitea path attempts a tea WRITE (tea pr comment) when a
+# comment parses, then falls back to the API. Hermeticity for this
+# wrapper comes from the FAILING stubs (exit 99), not from non-contact —
+# the arm above proves only parse acceptance and non-usage classification.
+# Parser-failure arms (1-4) remain zero-contact (asserted at 4b).
+
+echo "pr-edit.sh usage-contract regression passed (R1/R4)"
diff --git a/packages/mosaic/package.json b/packages/mosaic/package.json
index 425a2e15..3474ee79 100644
--- a/packages/mosaic/package.json
+++ b/packages/mosaic/package.json
@@ -25,7 +25,7 @@
     "lint": "eslint src",
     "typecheck": "tsc --noEmit",
     "test": "vitest run --passWithNoTests && pnpm run test:framework-shell",
-    "test:framework-shell": "bash framework/tools/quality/scripts/check-test-enumeration.sh && bash framework/tools/quality/scripts/test-check-test-enumeration.sh && python3 framework/tools/quality/scripts/test-framework-drift-check.py && bash framework/tools/quality/scripts/test-framework-drift-doctor.sh && bash framework/systemd/user/test-fleet-units.sh && python3 src/lease-broker/daemon_deadline_unittest.py && python3 src/lease-broker/normative_fragments_unittest.py && python3 src/lease-broker/promotion_binding_unittest.py && python3 src/lease-broker/promotion_trigger_unittest.py && python3 src/lease-broker/receipt_challenge_unittest.py && python3 src/lease-broker/context_recovery_unittest.py && python3 src/lease-broker/recovery_runtime_unittest.py && python3 src/lease-broker/recovery_b1_adversarial_unittest.py && python3 src/lease-broker/receipt_observer_client_unittest.py && python3 src/lease-broker/invariant_r_unittest.py && python3 src/lease-broker/framework_skill_portability_unittest.py && python3 src/lease-broker/revoke_noop_unittest.py && python3 src/mutator-gate/runtime_tools_unittest.py && python3 src/mutator-gate/runtime_launch_guard_unittest.py && python3 src/mutator-gate/version_coupling_unittest.py && python3 framework/tools/lease-broker/check-runtime-launches.py --root ../.. && bash framework/tools/codex/test-pr-diff-context.sh && bash framework/tools/qa/test-deps-preflight.sh && bash framework/tools/git/test-pr-edit.sh && bash framework/tools/git/test-pr-create-fallback-default-base.sh && bash framework/tools/git/test-repo-decl-consumption.sh && bash framework/tools/git/test-pr-review-gitea-comment.sh && bash framework/tools/git/test-pr-review-repo-host-override.sh && bash framework/tools/git/test-ci-queue-wait-no-status.sh && bash framework/tools/git/test-ci-queue-wait-branch-absent.sh && bash framework/tools/git/test-ci-queue-wait-tristate.sh && bash framework/tools/git/test-ci-queue-wait-github-checks.sh && bash framework/tools/git/test-ci-queue-wait-no-ci-expected.sh && bash framework/tools/git/test-pr-merge-queue-branch.sh && bash framework/tools/git/test-pr-merge-no-ci-expected.sh && bash framework/tools/git/test-pr-merge-fork-ci-status.sh && bash framework/tools/git/test-pr-merge-head-pin.sh && bash framework/tools/git/test-pr-merge-message-field.sh && bash framework/tools/git/test-git-credential-mosaic.sh && bash framework/tools/git/test-gitea-token-identity.sh && bash framework/tools/git/test-issue-comment-usage-contract.sh && bash framework/tools/git/test-issue-comment-readback.sh && bash framework/tools/git/test-issue-close-usage-contract.sh && bash framework/tools/git/test-issue-reopen-usage-contract.sh && bash framework/tools/git/test-pr-close-usage-contract.sh && bash framework/tools/git/test-pr-review-usage-contract.sh && bash framework/tools/git/test-issue-edit-usage-contract.sh && bash framework/tools/git/test-issue-create-usage-contract.sh && bash framework/tools/git/test-explain-diagnostic-status-neutral.sh && bash framework/tools/git/test-detect-platform-outside-repo.sh && bash framework/tools/woodpecker/test-terminal-green-contract.sh && bash framework/tools/_scripts/test-install-ordering-guard.sh && bash framework/tools/_scripts/test-mosaic-init-rce.sh && bash framework/tools/tmux/agent-send.test.sh && bash framework/tools/wake/test-wake-store-ack.sh && bash framework/tools/wake/test-wake-store-enqueue-race.sh && bash framework/tools/wake/test-wake-digest-hmac.sh && bash framework/tools/wake/test-wake-digest-quarantine.sh && bash framework/tools/wake/test-wake-detector.sh && bash framework/tools/wake/test-wake-fn-oracle.sh && bash framework/tools/wake/test-wake-reconcile.sh && bash framework/tools/wake/test-wake-beacon.sh && bash framework/tools/wake/test-wake-preimage.sh && bash framework/tools/wake/test-wake-install.sh && bash framework/tools/glpi/test-list-http-status.sh && bash framework/tools/orchestrator/test-board-roll.sh && bash framework/tools/woodpecker/test-ci-wait-exit-matrix.sh && bash framework/tools/_scripts/test-fleet-transport-check.sh && bash framework/tools/_scripts/test-brain-home-check.sh && bash framework/tools/_scripts/test-structure-anchor-check.sh && bash framework/tools/fleet/test-agent-session-broker-preflight.sh && bash framework/tools/fleet/test-agent-session-legacy-socket-guard.sh && bash framework/tools/git/test-grant-reviewer.sh"
+    "test:framework-shell": "bash framework/tools/quality/scripts/check-test-enumeration.sh && bash framework/tools/quality/scripts/test-check-test-enumeration.sh && python3 framework/tools/quality/scripts/test-framework-drift-check.py && bash framework/tools/quality/scripts/test-framework-drift-doctor.sh && bash framework/systemd/user/test-fleet-units.sh && python3 src/lease-broker/daemon_deadline_unittest.py && python3 src/lease-broker/normative_fragments_unittest.py && python3 src/lease-broker/promotion_binding_unittest.py && python3 src/lease-broker/promotion_trigger_unittest.py && python3 src/lease-broker/receipt_challenge_unittest.py && python3 src/lease-broker/context_recovery_unittest.py && python3 src/lease-broker/recovery_runtime_unittest.py && python3 src/lease-broker/recovery_b1_adversarial_unittest.py && python3 src/lease-broker/receipt_observer_client_unittest.py && python3 src/lease-broker/invariant_r_unittest.py && python3 src/lease-broker/framework_skill_portability_unittest.py && python3 src/lease-broker/revoke_noop_unittest.py && python3 src/mutator-gate/runtime_tools_unittest.py && python3 src/mutator-gate/runtime_launch_guard_unittest.py && python3 src/mutator-gate/version_coupling_unittest.py && python3 framework/tools/lease-broker/check-runtime-launches.py --root ../.. && bash framework/tools/codex/test-pr-diff-context.sh && bash framework/tools/qa/test-deps-preflight.sh && bash framework/tools/git/test-pr-edit.sh && bash framework/tools/git/test-pr-create-fallback-default-base.sh && bash framework/tools/git/test-repo-decl-consumption.sh && bash framework/tools/git/test-pr-review-gitea-comment.sh && bash framework/tools/git/test-pr-review-repo-host-override.sh && bash framework/tools/git/test-ci-queue-wait-no-status.sh && bash framework/tools/git/test-ci-queue-wait-branch-absent.sh && bash framework/tools/git/test-ci-queue-wait-tristate.sh && bash framework/tools/git/test-ci-queue-wait-github-checks.sh && bash framework/tools/git/test-ci-queue-wait-no-ci-expected.sh && bash framework/tools/git/test-pr-merge-queue-branch.sh && bash framework/tools/git/test-pr-merge-no-ci-expected.sh && bash framework/tools/git/test-pr-merge-fork-ci-status.sh && bash framework/tools/git/test-pr-merge-head-pin.sh && bash framework/tools/git/test-pr-merge-message-field.sh && bash framework/tools/git/test-git-credential-mosaic.sh && bash framework/tools/git/test-gitea-token-identity.sh && bash framework/tools/git/test-issue-comment-usage-contract.sh && bash framework/tools/git/test-issue-comment-readback.sh && bash framework/tools/git/test-issue-close-usage-contract.sh && bash framework/tools/git/test-issue-reopen-usage-contract.sh && bash framework/tools/git/test-pr-close-usage-contract.sh && bash framework/tools/git/test-pr-review-usage-contract.sh && bash framework/tools/git/test-issue-edit-usage-contract.sh && bash framework/tools/git/test-issue-create-usage-contract.sh && bash framework/tools/git/test-pr-edit-usage-contract.sh && bash framework/tools/git/test-explain-diagnostic-status-neutral.sh && bash framework/tools/git/test-detect-platform-outside-repo.sh && bash framework/tools/woodpecker/test-terminal-green-contract.sh && bash framework/tools/_scripts/test-install-ordering-guard.sh && bash framework/tools/_scripts/test-mosaic-init-rce.sh && bash framework/tools/tmux/agent-send.test.sh && bash framework/tools/wake/test-wake-store-ack.sh && bash framework/tools/wake/test-wake-store-enqueue-race.sh && bash framework/tools/wake/test-wake-digest-hmac.sh && bash framework/tools/wake/test-wake-digest-quarantine.sh && bash framework/tools/wake/test-wake-detector.sh && bash framework/tools/wake/test-wake-fn-oracle.sh && bash framework/tools/wake/test-wake-reconcile.sh && bash framework/tools/wake/test-wake-beacon.sh && bash framework/tools/wake/test-wake-preimage.sh && bash framework/tools/wake/test-wake-install.sh && bash framework/tools/glpi/test-list-http-status.sh && bash framework/tools/orchestrator/test-board-roll.sh && bash framework/tools/woodpecker/test-ci-wait-exit-matrix.sh && bash framework/tools/_scripts/test-fleet-transport-check.sh && bash framework/tools/_scripts/test-brain-home-check.sh && bash framework/tools/_scripts/test-structure-anchor-check.sh && bash framework/tools/fleet/test-agent-session-broker-preflight.sh && bash framework/tools/fleet/test-agent-session-legacy-socket-guard.sh && bash framework/tools/git/test-grant-reviewer.sh"
   },
   "dependencies": {
     "@mosaicstack/brain": "workspace:*",