diff --git a/bin/fm-brief.sh b/bin/fm-brief.sh
index 700c743ca14..84e5cc5480f 100755
--- a/bin/fm-brief.sh
+++ b/bin/fm-brief.sh
@@ -45,6 +45,10 @@
 # affected-based test selection before done, a learning loop into the project's
 # docs/agents/codegraph/README.md with an AGENTS.md pointer, and a one-line note
 # to continue without codegraph when the binary is missing.
+# They also carry a standing test-selection contract: no full-suite first run,
+# changed-first selection (fm-test-run.sh --changed here, the project runner's
+# native equivalent elsewhere), failed-family-only reruns, GitHub CI as the PR
+# merge verdict, and full output kept in a file so failures need no rerun.
 # Ship briefs begin with a worktree-isolation assertion before the branch step.
 # --mode is refused on scout and secondmate scaffolds: a scout's deliverable is a
 # report rather than a merge, and a charter is not a delivery contract.
@@ -317,6 +321,16 @@ CODEGRAPH_SECTION=$(printf '%s\n' \
 "   Keep an \`AGENTS.md\` pointer section to that file via '$FM_ROOT/bin/fm-ensure-agents-md.sh .'" \
 'If the `codegraph` binary is missing, append one status line noting it and continue with ordinary tools; nothing else changes.')
 
+# Standing test-selection contract shared by the ship and scout scaffolds.
+# shellcheck disable=SC2016  # single quotes are deliberate: backtick-wrapped command names must reach the reading agent verbatim, not expand at scaffold time.
+TEST_SELECTION_SECTION=$(printf '%s\n' \
+'# Test selection contract' \
+'Verify efficiently: never make a full local suite run your first verification step.' \
+"1. Changed-first selection: when the repo under test is the firstmate repo itself, select tests with \`bin/fm-test-run.sh --changed\` (add \`--base <ref>\` when your working base is not origin/main); on other projects use the runner's native changed/related feature, e.g. \`vitest --changed\`." \
+'2. On failure, re-run only the failed family or single script (`bin/fm-test-run.sh --family <name>` or that one script path), never the whole suite.' \
+'3. For PR-based deliveries, GitHub CI owns the final merge verdict; local runs are a fast pre-check, not the authority.' \
+'4. Keep full test output in a file: never pipe it through `tail` or any other filter that discards per-test result lines, so failures stay identifiable without rerunning.')
+
 if [ "$KIND" = scout ]; then
 cat > "$BRIEF" <<EOF
 You are a crewmate: an autonomous worker agent managed by firstmate. Work on your own; do not wait for a human.
@@ -357,6 +371,8 @@ The report is the only thing that survives, so anything worth keeping must be in
 
 $CODEGRAPH_SECTION
 
+$TEST_SELECTION_SECTION
+
 # Definition of done
 Write your findings to \`$DATA/$ID/report.md\`.
 The report must stand alone: what you did, what you found, the evidence (commands run, output, file:line references), and what you recommend.
@@ -476,6 +492,8 @@ $RULE1
 
 $CODEGRAPH_SECTION
 
+$TEST_SELECTION_SECTION
+
 # Project memory
 If \`AGENTS.md\` or \`CLAUDE.md\` already exists, or if this task produced durable project-intrinsic knowledge, run \`$FM_ROOT/bin/fm-ensure-agents-md.sh .\` in the worktree.
 Record only project knowledge useful to almost every future session.
diff --git a/tests/fm-brief.test.sh b/tests/fm-brief.test.sh
index 11371572bd7..4b698f3ac4b 100755
--- a/tests/fm-brief.test.sh
+++ b/tests/fm-brief.test.sh
@@ -70,6 +70,46 @@ test_codegraph_contract_in_ship_and_scout_briefs() {
   pass "fm-brief.sh: ship and scout scaffolds carry the standing CodeGraph usage contract"
 }
 
+# Ship and scout scaffolds carry a standing test-selection contract; a
+# secondmate charter supervises its own crews and must not carry this worker
+# contract.
+test_test_selection_contract_in_ship_and_scout_briefs() {
+  local home id kind brief
+  home="$TMP_ROOT/testsel-home"
+  mkdir -p "$home/data"
+  for kind in ship scout; do
+    id="brief-testsel-$kind"
+    if [ "$kind" = scout ]; then
+      FM_HOME="$home" FM_ROOT_OVERRIDE="$ROOT" "$ROOT/bin/fm-brief.sh" "$id" some-proj --scout >/dev/null 2>&1
+    else
+      FM_HOME="$home" FM_ROOT_OVERRIDE="$ROOT" "$ROOT/bin/fm-brief.sh" "$id" some-proj --mode direct-PR >/dev/null 2>&1
+    fi
+    brief="$home/data/$id/brief.md"
+    assert_grep "# Test selection contract" "$brief" \
+      "$kind brief missing the test-selection contract heading"
+    assert_grep "never make a full local suite run your first verification step" "$brief" \
+      "$kind brief missing the no-full-suite-first rule"
+    assert_grep "select tests with \`bin/fm-test-run.sh --changed\` (add \`--base <ref>\` when your working base is not origin/main)" "$brief" \
+      "$kind brief missing changed-first selection for the firstmate repo"
+    assert_grep "on other projects use the runner's native changed/related feature" "$brief" \
+      "$kind brief missing the other-projects changed-selection rule"
+    assert_grep "re-run only the failed family or single script (\`bin/fm-test-run.sh --family <name>\` or that one script path), never the whole suite" "$brief" \
+      "$kind brief missing the failed-family-only rerun rule"
+    assert_grep "GitHub CI owns the final merge verdict; local runs are a fast pre-check, not the authority" "$brief" \
+      "$kind brief missing the CI-owns-the-verdict rule"
+    assert_grep "never pipe it through \`tail\` or any other filter that discards per-test result lines" "$brief" \
+      "$kind brief missing the keep-full-output rule"
+    assert_no_grep "EOF" "$brief" \
+      "$kind brief leaked a heredoc EOF marker (unterminated heredoc) in the test-selection section"
+  done
+
+  FM_HOME="$home" FM_SECONDMATE_CHARTER='sample domain' \
+    "$ROOT/bin/fm-brief.sh" brief-testsel-mate --secondmate --no-projects >/dev/null 2>&1
+  assert_no_grep "# Test selection contract" "$home/data/brief-testsel-mate/brief.md" \
+    "secondmate charter must not carry the worker-level test-selection contract"
+  pass "fm-brief.sh: ship and scout scaffolds carry the standing test-selection contract"
+}
+
 test_script_parses() {
   local out rc
   out=$(bash -n "$ROOT/bin/fm-brief.sh" 2>&1); rc=$?
@@ -771,6 +811,7 @@ test_herdr_lab_contract_quotes_foreign_firstmate_path
 test_herdr_lab_omission_is_loud_for_ship_and_scout
 test_herdr_lab_contract_applies_to_scouts_but_not_secondmates
 test_codegraph_contract_in_ship_and_scout_briefs
+test_test_selection_contract_in_ship_and_scout_briefs
 test_secondmate_no_projects_charter
 test_secondmate_marked_request_reporting_contract
 test_secondmate_directory_paths_are_absolute_and_output_is_stable