diff --git a/.agents/pipelines/impl-issue.yaml b/.agents/pipelines/impl-issue.yaml
index 398d717e7..6e81e84ab 100644
--- a/.agents/pipelines/impl-issue.yaml
+++ b/.agents/pipelines/impl-issue.yaml
@@ -233,6 +233,11 @@ steps:
           command: "{{ project.contract_test_command }}"
           must_pass: true
           on_failure: fail
+        - type: test_diff
+          on_failure: rework
+        - type: test_count_baseline
+          base_ref: HEAD~1
+          on_failure: rework
         - type: agent_review
           persona: navigator
           criteria_path: .agents/contracts/impl-review-criteria.md
diff --git a/internal/contract/contract.go b/internal/contract/contract.go
index 7dc862f96..253f5c05f 100644
--- a/internal/contract/contract.go
+++ b/internal/contract/contract.go
@@ -63,6 +63,9 @@ type ContractConfig struct {
 	TestFilePattern  []string `json:"test_file_pattern,omitempty"  yaml:"test_file_pattern,omitempty"`  // Pathspecs (e.g. ["*_test.go"], ["**/test_*.py"], ["**/*.test.ts"])
 	TestFuncPattern  string   `json:"test_func_pattern,omitempty"  yaml:"test_func_pattern,omitempty"`  // Regex matching one test declaration per line
 
+	// test_count_baseline contract fields — post-commit defense-in-depth alongside test_diff.
+	BaseRef string `json:"base_ref,omitempty" yaml:"base_ref,omitempty"` // Git ref to compare HEAD against (default HEAD~1)
+
 	// event_contains contract fields — validated by executor (needs event store access)
 	Events []EventPattern `json:"events,omitempty" yaml:"events,omitempty"` // Expected event patterns to match against the step's event log
 
@@ -130,6 +133,8 @@ func NewValidator(cfg ContractConfig) ContractValidator {
 		return &sourceDiffValidator{}
 	case "test_diff":
 		return &testDiffValidator{}
+	case "test_count_baseline":
+		return &testCountBaselineValidator{}
 	case "agent_review":
 		// agent_review requires an adapter runner — NewValidator returns nil.
 		// The executor uses ValidateWithRunner() instead for this type.
diff --git a/internal/contract/test_count_baseline.go b/internal/contract/test_count_baseline.go
new file mode 100644
index 000000000..ed1789e3d
--- /dev/null
+++ b/internal/contract/test_count_baseline.go
@@ -0,0 +1,109 @@
+package contract
+
+import (
+	"bytes"
+	"fmt"
+	"os/exec"
+	"path"
+	"regexp"
+	"strings"
+)
+
+// testCountBaselineValidator is the post-commit "last line of defense"
+// against test deletions. Where test_diff inspects the working-tree
+// diff, this one compares COMMITTED tree counts: HEAD vs BaseRef
+// (default HEAD~1). Catches deletions that slipped past diff inspection
+// (file moves, force-pushes within session, multi-commit sequences).
+//
+// Language-agnostic: shares TestFilePattern + TestFuncPattern with
+// test_diff so a project configures patterns once.
+//
+// Operation:
+//  1. `git ls-tree -r --name-only <ref>` → filter by TestFilePattern globs
+//  2. `git show <ref>:<path>` per file → count regex matches
+//  3. Fail if (base - head) > MaxTestDeletions
+type testCountBaselineValidator struct{}
+
+func (v *testCountBaselineValidator) Validate(cfg ContractConfig, workspacePath string) error {
+	baseRef := cfg.BaseRef
+	if baseRef == "" {
+		baseRef = "HEAD~1"
+	}
+	max := cfg.MaxTestDeletions
+
+	globs := cfg.TestFilePattern
+	if len(globs) == 0 {
+		globs = []string{defaultTestFilePathspec}
+	}
+	patternStr := cfg.TestFuncPattern
+	if patternStr == "" {
+		patternStr = defaultTestFuncPattern
+	}
+	re, err := regexp.Compile(patternStr)
+	if err != nil {
+		return fmt.Errorf("test_count_baseline: invalid TestFuncPattern %q: %w", patternStr, err)
+	}
+
+	headCount, err := countTestFuncsAtRef(workspacePath, "HEAD", globs, re)
+	if err != nil {
+		return nil
+	}
+	baseCount, err := countTestFuncsAtRef(workspacePath, baseRef, globs, re)
+	if err != nil {
+		return nil
+	}
+
+	net := baseCount - headCount
+	if net > max {
+		return fmt.Errorf("test_count_baseline: HEAD has %d test declarations vs %s=%d (net deletion %d, max allowed %d); persona must replace removed tests, not net-delete them across commits",
+			headCount, baseRef, baseCount, net, max)
+	}
+	return nil
+}
+
+func countTestFuncsAtRef(dir, ref string, globs []string, re *regexp.Regexp) (int, error) {
+	out, err := runGitCmd(dir, "ls-tree", "-r", "--name-only", ref)
+	if err != nil {
+		return 0, err
+	}
+	total := 0
+	for _, p := range strings.Split(strings.TrimSpace(out), "\n") {
+		if p == "" || !matchesAnyGlob(p, globs) {
+			continue
+		}
+		blob, err := runGitCmd(dir, "show", ref+":"+p)
+		if err != nil {
+			continue
+		}
+		total += len(re.FindAllString(blob, -1))
+	}
+	return total, nil
+}
+
+// matchesAnyGlob checks both the full path and the basename against each
+// pattern. path.Match doesn't grok `**`, so basename match is a
+// pragmatic fallback covering `*_test.go`, `test_*.py`, `*.test.ts`, etc.
+func matchesAnyGlob(p string, globs []string) bool {
+	base := path.Base(p)
+	for _, g := range globs {
+		if ok, _ := path.Match(g, p); ok {
+			return true
+		}
+		if ok, _ := path.Match(g, base); ok {
+			return true
+		}
+	}
+	return false
+}
+
+func runGitCmd(dir string, args ...string) (string, error) {
+	cmd := exec.Command("git", args...)
+	cmd.Dir = dir
+	var out bytes.Buffer
+	cmd.Stdout = &out
+	cmd.Stderr = &bytes.Buffer{}
+	if err := cmd.Run(); err != nil {
+		return "", err
+	}
+	return out.String(), nil
+}
diff --git a/internal/contract/test_count_baseline_test.go b/internal/contract/test_count_baseline_test.go
new file mode 100644
index 000000000..b31ea5800
--- /dev/null
+++ b/internal/contract/test_count_baseline_test.go
@@ -0,0 +1,145 @@
+package contract
+
+import (
+	"testing"
+)
+
+// initRepoTwoCommits seeds a repo with one *_test.go (2 tests), commits,
+// then optionally mutates and recommits. Returns the dir.
+func initRepoTwoCommits(t *testing.T, mutate func(dir string)) string {
+	t.Helper()
+	dir := t.TempDir()
+	runGit(t, dir, "init", "-q")
+	writeFile(t, dir, "x_test.go", `package x
+
+import "testing"
+
+func TestAlpha(t *testing.T) { _ = t }
+func TestBeta(t *testing.T) { _ = t }
+`)
+	runGit(t, dir, "add", "x_test.go")
+	runGit(t, dir, "commit", "-q", "-m", "base")
+	if mutate != nil {
+		mutate(dir)
+		runGit(t, dir, "add", "-A")
+		runGit(t, dir, "commit", "-q", "-m", "head")
+	}
+	return dir
+}
+
+func TestTestCountBaseline_NoChange_Passes(t *testing.T) {
+	dir := initRepoTwoCommits(t, func(d string) {
+		writeFile(t, d, "y.go", `package x
+`)
+	})
+	v := &testCountBaselineValidator{}
+	if err := v.Validate(ContractConfig{Type: "test_count_baseline"}, dir); err != nil {
+		t.Fatalf("expected pass, got: %v", err)
+	}
+}
+
+func TestTestCountBaseline_Addition_Passes(t *testing.T) {
+	dir := initRepoTwoCommits(t, func(d string) {
+		writeFile(t, d, "x_test.go", `package x
+
+import "testing"
+
+func TestAlpha(t *testing.T) { _ = t }
+func TestBeta(t *testing.T) { _ = t }
+func TestGamma(t *testing.T) { _ = t }
+`)
+	})
+	v := &testCountBaselineValidator{}
+	if err := v.Validate(ContractConfig{Type: "test_count_baseline"}, dir); err != nil {
+		t.Fatalf("expected pass on addition, got: %v", err)
+	}
+}
+
+func TestTestCountBaseline_Deletion_Fails(t *testing.T) {
+	dir := initRepoTwoCommits(t, func(d string) {
+		writeFile(t, d, "x_test.go", `package x
+
+import "testing"
+
+func TestAlpha(t *testing.T) { _ = t }
+`)
+	})
+	v := &testCountBaselineValidator{}
+	if err := v.Validate(ContractConfig{Type: "test_count_baseline"}, dir); err == nil {
+		t.Fatal("expected error on deletion, got nil")
+	}
+}
+
+func TestTestCountBaseline_FileMove_NetsZero(t *testing.T) {
+	dir := initRepoTwoCommits(t, func(d string) {
+		// Delete x_test.go, recreate same tests under different filename.
+		runGit(t, d, "rm", "-q", "x_test.go")
+		writeFile(t, d, "renamed_test.go", `package x
+
+import "testing"
+
+func TestAlpha(t *testing.T) { _ = t }
+func TestBeta(t *testing.T) { _ = t }
+`)
+	})
+	v := &testCountBaselineValidator{}
+	if err := v.Validate(ContractConfig{Type: "test_count_baseline"}, dir); err != nil {
+		t.Fatalf("expected pass on file move, got: %v", err)
+	}
+}
+
+func TestTestCountBaseline_HigherTolerance_Passes(t *testing.T) {
+	dir := initRepoTwoCommits(t, func(d string) {
+		writeFile(t, d, "x_test.go", `package x
+`)
+	})
+	v := &testCountBaselineValidator{}
+	cfg := ContractConfig{Type: "test_count_baseline", MaxTestDeletions: 2}
+	if err := v.Validate(cfg, dir); err != nil {
+		t.Fatalf("expected pass with tolerance=2, got: %v", err)
+	}
+}
+
+func TestTestCountBaseline_NoBaseRef_PassesSilently(t *testing.T) {
+	// Single-commit repo — HEAD~1 doesn't resolve.
+	dir := initRepoTwoCommits(t, nil)
+	v := &testCountBaselineValidator{}
+	if err := v.Validate(ContractConfig{Type: "test_count_baseline"}, dir); err != nil {
+		t.Fatalf("expected silent pass without base ref, got: %v", err)
+	}
+}
+
+func TestTestCountBaseline_PythonConfig_DetectsDeletion(t *testing.T) {
+	dir := t.TempDir()
+	runGit(t, dir, "init", "-q")
+	writeFile(t, dir, "test_things.py", `def test_alpha():
+    pass
+
+def test_beta():
+    pass
+`)
+	runGit(t, dir, "add", "-A")
+	runGit(t, dir, "commit", "-q", "-m", "base")
+	writeFile(t, dir, "test_things.py", `def test_alpha():
+    pass
+`)
+	runGit(t, dir, "add", "-A")
+	runGit(t, dir, "commit", "-q", "-m", "head")
+	v := &testCountBaselineValidator{}
+	cfg := ContractConfig{
+		Type:            "test_count_baseline",
+		TestFilePattern: []string{"test_*.py", "*_test.py"},
+		TestFuncPattern: `(?m)^[ \t]*def[ \t]+test_\w+`,
+	}
+	if err := v.Validate(cfg, dir); err == nil {
+		t.Fatal("expected error for python deletion, got nil")
+	}
+}
+
+func TestTestCountBaseline_NoGit_PassesSilently(t *testing.T) {
+	dir := t.TempDir()
+	v := &testCountBaselineValidator{}
+	if err := v.Validate(ContractConfig{Type: "test_count_baseline"}, dir); err != nil {
+		t.Fatalf("expected silent pass without git, got: %v", err)
+	}
+}
diff --git a/internal/contract/test_diff.go b/internal/contract/test_diff.go
index fecde4db5..cc144b075 100644
--- a/internal/contract/test_diff.go
+++ b/internal/contract/test_diff.go
@@ -26,7 +26,7 @@ type testDiffValidator struct{}
 
 const (
 	defaultTestFilePathspec = "*_test.go"
-	defaultTestFuncPattern  = `^[ \t]*func[ \t]+(Test|Example|Benchmark|Fuzz)[A-Za-z0-9_]*\b`
+	defaultTestFuncPattern  = `(?m)^[ \t]*func[ \t]+(Test|Example|Benchmark|Fuzz)[A-Za-z0-9_]*\b`
 )
 
 func (v *testDiffValidator) Validate(cfg ContractConfig, workspacePath string) error {
diff --git a/internal/defaults/embedfs/pipelines/impl-issue.yaml b/internal/defaults/embedfs/pipelines/impl-issue.yaml
index 64a415d73..43fdeba1e 100644
--- a/internal/defaults/embedfs/pipelines/impl-issue.yaml
+++ b/internal/defaults/embedfs/pipelines/impl-issue.yaml
@@ -233,6 +233,11 @@ steps:
           command: "{{ project.contract_test_command }}"
           must_pass: true
           on_failure: fail
+        - type: test_diff
+          on_failure: rework
+        - type: test_count_baseline
+          base_ref: HEAD~1
+          on_failure: rework
         - type: agent_review
           persona: navigator
           criteria_path: .agents/contracts/impl-review-criteria.md
diff --git a/internal/manifest/types.go b/internal/manifest/types.go
index 80c1cc819..2523831d7 100644
--- a/internal/manifest/types.go
+++ b/internal/manifest/types.go
@@ -26,6 +26,8 @@ type Project struct {
 	BuildCommand        string                   `yaml:"build_command,omitempty"`
 	FormatCommand       string                   `yaml:"format_command,omitempty"`
 	SourceGlob          string                   `yaml:"source_glob,omitempty"`
+	TestFilePattern     []string                 `yaml:"test_file_pattern,omitempty"` // test_diff / test_count_baseline pathspecs (#1583, #1584)
+	TestFuncPattern     string                   `yaml:"test_func_pattern,omitempty"` // test_diff / test_count_baseline regex (#1583, #1584)
 	Skill               string                   `yaml:"skill,omitempty"`
 	Services            map[string]ServiceConfig `yaml:"services,omitempty"`
 }
diff --git a/wave.yaml b/wave.yaml
index 74e725d62..9e3a6a250 100644
--- a/wave.yaml
+++ b/wave.yaml
@@ -14,6 +14,12 @@ project:
     lint_command: "go vet ./..."
     build_command: "go build ./..."
     source_glob: "*.go"
+    # test_diff / test_count_baseline contracts (#1583, #1584): how to
+    # spot test declarations in this codebase. Defaults already match
+    # Go, but make it explicit so non-Go projects know the knobs.
+    test_file_pattern:
+        - "*_test.go"
+    test_func_pattern: '(?m)^[ \t]*func[ \t]+(Test|Example|Benchmark|Fuzz)[A-Za-z0-9_]*\b'
 adapters:
     claude:
         binary: claude