diff --git a/test/phase-b-h.test.js b/test/phase-b-h.test.js
index 56d6fee..32703f8 100644
--- a/test/phase-b-h.test.js
+++ b/test/phase-b-h.test.js
@@ -2645,6 +2645,21 @@ test('D5†: dropping the unavailable sentence makes D5 red', async () => {
 
 // ── F8: a mis-sized vector is a HARD error when the width is declared ──────
 //
+// ★ The positive predicate below is shared by the unmutated case and by every
+// F8 mutant, so a mutant can only pass by satisfying the SAME requirement the
+// real code satisfies. Re-writing the requirement inside the mutant's body
+// ("under the mutation the bad vector lands") is a self-test: it asserts the
+// mutated behaviour and therefore stays green exactly when the criterion should
+// fail.
+function assertExplicitWidthRefused(store) {
+  assert.throws(
+    () => store.putBlock({ text: 'x', vector: [1, 2], fingerprint: 'fp-a', expectedDimension: 3 }),
+    (err) => /dimension 2 does not match the active space's 3/.test(err.message),
+    'a 2-wide vector in a 3-wide space must be refused, not stored and counted later',
+  )
+  assert.equal(store.countBlocks(), 0, 'nothing was written')
+}
+//
 // criteria:165 says "provider returns a dimension ≠ the configured one ⇒ hard
 // error, never truncate or pad". Until now only the adapter layer enforced it
 // (H3b); the write path silently degraded, so a bad vector could land and be
@@ -2655,12 +2670,7 @@ test('D5†: dropping the unavailable sentence makes D5 red', async () => {
 test('F8: putBlock refuses a vector whose width differs from the declared space', () => {
   const store = new BlockStore({ path: ':memory:' }).open()
   try {
-    assert.throws(
-      () => store.putBlock({ text: 'x', vector: [1, 2], fingerprint: 'fp-a', expectedDimension: 3 }),
-      /dimension 2 does not match the active space's 3/,
-      'a 2-wide vector in a 3-wide space must be refused, not stored and counted later',
-    )
-    assert.equal(store.countBlocks(), 0, 'nothing was written')
+    assertExplicitWidthRefused(store)
 
     // The matching width is accepted.
     assert.equal(
@@ -2710,13 +2720,28 @@ test('F8: a provider returning the wrong width still degrades (not a caller bug)
   try {
     const r = await mem.commit({ text: 'x' })
     assert.equal(r.embedded, false, 'a misbehaving provider degrades, it does not throw')
+    // ★ Counting rows, not picking one: `allBlocks(1)[0]` is satisfied by any
+    // single row, so a regression that stopped writing on the degraded path
+    // entirely would still be green here. F8/W4 require the block to LAND.
+    assert.equal(mem.store.countBlocks(), 1, 'the block is still written (degrade ≠ drop)')
     assert.equal(mem.store.allBlocks(1)[0].vector, '', 'and no bad vector is stored')
   } finally {
     await done()
   }
 })
 
-test('F8†: softening the write-side width check lets a bad vector land', async () => {
+test('F8†: softening the write-side width check bites the positive criterion red', async (t) => {
+  // ★ The anchor must appear EXACTLY ONCE in lib/store.js. `withMutatedCopy`
+  // already fails loudly when it is missing; the count check makes "appears
+  // twice, first match mutated, second silently left intact" impossible too.
+  const { readFileSync } = await import('node:fs')
+  const source = readFileSync(new URL('../lib/store.js', import.meta.url), 'utf8')
+  assert.equal(
+    source.split('      if (actual !== expectedDimension) {').length - 1,
+    1,
+    'the F8† anchor must occur exactly once in lib/store.js',
+  )
+
   await withMutatedCopy(
     'store.js',
     [[
@@ -2726,14 +2751,19 @@ test('F8†: softening the write-side width check lets a bad vector land', async
     async (mod) => {
       const store = new mod.BlockStore({ path: ':memory:' }).open()
       try {
-        // Under the mutation the bad vector is accepted, which is the state F8 forbids.
-        const written = store.putBlock({ text: 'x', vector: [1, 2], fingerprint: 'fp-a', expectedDimension: 3 })
-        assert.equal(written.created, true, 'the mutation really admits the wrong width')
-        assert.equal(
-          JSON.parse(store.allBlocks(1)[0].vector).length,
-          2,
-          'and stores it — so F8 (which requires a throw) fails on the mutated module',
-        )
+        // ★ The SAME positive criterion, run on the mutant. It must throw: on the
+        // mutant the write is admitted, so `assert.throws` sees no error and
+        // fails with ERR_ASSERTION.
+        assert.throws(() => assertExplicitWidthRefused(store), (err) => {
+          assert.equal(err.code, 'ERR_ASSERTION', 'the criterion must fail as an assertion')
+          t.diagnostic(`F8† RAW RED >>> ${String(err.message).split('\n')[0]}`)
+          return true
+        }, 'F8† must break the unchanged F8 criterion')
+        // Corroboration: the mutation really does admit the bad vector. This is
+        // reported as a diagnostic, never as the thing that "bites" — asserting
+        // it would be the self-test that made the previous version useless.
+        const probe = store.putBlock({ text: 'probe', vector: [1, 2], fingerprint: 'fp-a', expectedDimension: 3 })
+        t.diagnostic(`F8† mutant admitted the bad vector: created=${probe.created}, blocks=${store.countBlocks()}`)
       } finally {
         store.close()
       }
@@ -2741,6 +2771,60 @@ test('F8†: softening the write-side width check lets a bad vector land', async
   )
 })
 
+test('F8†b: a degraded provider write that drops the block bites countBlocks red', async (t) => {
+  // ★ Mutation on lib/index.js: the degraded branch (provider returned a wrong
+  // width) stops persisting. `embedded === false` and `vector === ''` both stay
+  // green under this mutation — only the row count catches it, which is exactly
+  // what the `allBlocks(1)[0]` shape could not do.
+  await withMutatedCopy(
+    'index.js',
+    [[
+      `    if (!Array.isArray(vector) || vector.length !== space.dimension) {
+      return { ...this.store.putBlock(input), embedded: false }
+    }`,
+      `    if (!Array.isArray(vector) || vector.length !== space.dimension) {
+      return { id: '', created: false, embedded: false } // MUTATED: degrade by dropping
+    }`,
+    ]],
+    async (mod) => {
+      const { Context } = await import('@deepseek-ai/cordis')
+      const { SystemPrompt } = await import('@deepseek-ai/dsh-system-prompt')
+      const { ToolRuntime } = await import('@deepseek-ai/dsh-tools')
+      const { mkdtempSync, rmSync } = await import('node:fs')
+      const { tmpdir } = await import('node:os')
+      const { join } = await import('node:path')
+      const dir = mkdtempSync(join(tmpdir(), 'f8b-'))
+      const ctx = new Context()
+      new SystemPrompt(ctx, {})
+      new ToolRuntime(ctx, {})
+      try {
+        const mem = mod.apply(ctx, {
+          path: join(dir, 'm.db'),
+          embedder: { async embedText() { return [1, 2] }, info: () => ({ fingerprint: 'fp-x', dimension: 3 }) },
+        })
+        const r = await mem.commit({ text: 'x' })
+        // The two assertions that survive the mutation — reported, not relied on.
+        t.diagnostic(`F8†b still-green under mutation: embedded=${r.embedded}, blocks=${mem.store.countBlocks()}`)
+        assert.throws(() => {
+          assert.equal(
+            mem.store.countBlocks(),
+            1,
+            'the block must still be written on a degraded provider write',
+          )
+          assert.equal(mem.store.allBlocks(1)[0]?.vector, '', 'and carry no bad vector')
+        }, (err) => {
+          assert.equal(err.code, 'ERR_ASSERTION', 'only the row-count criterion may bite')
+          t.diagnostic(`F8†b RAW RED >>> ${String(err.message).split('\n')[0]}`)
+          return true
+        }, 'F8†b must break the unchanged provider-degradation criterion')
+      } finally {
+        await ctx.fiber.dispose()
+        rmSync(dir, { recursive: true, force: true })
+      }
+    },
+  )
+})
+
 test('F3 performance guard: blockStates source does not parse vector payloads on reads', async () => {
   // The old implementation did `JSON.parse(row.vector).length` for every row;
   // at 2000 blocks x 2048 dims that measured ~354ms per renderIndex call, ~255ms