diff --git a/docs/changelog/2026-08-24-debt-flakes-c100.md b/docs/changelog/2026-08-24-debt-flakes-c100.md
new file mode 100644
index 00000000..3f478d14
--- /dev/null
+++ b/docs/changelog/2026-08-24-debt-flakes-c100.md
@@ -0,0 +1,16 @@
+# DEBT-FLAKES-C100 — fix flakes pré-existentes do C100 (Closes #553)
+
+Duas flaky tests do pipeline de sugestões de campanha (E11) e do maquinário de
+lease de consentimento, ambas pré-existentes ao PR C100:
+
+1. **campaignSuggestions silence review** — amostra de 10 municípios insuficiente
+   sob carga paralela (P(fail) nominal 0,17%). Amostra ampliada para 30
+   (P(fail) ≈ 7e-9) com mensagem de diagnóstico.
+
+2. **testDatabaseLease concurrent ensures** — TOCTOU find→create em
+   `ensureLeasedConsent` permitia 2 creates sob advisory lock extremo.
+   Tornado idempotente via `INSERT … ON CONFLICT (key) DO NOTHING` +
+   find, eliminando a corrida independente do lock.
+
+Mudanças: `tests/helpers/testDatabaseLease.ts`,
+`tests/int/campaignSuggestions.int.spec.ts`.
diff --git a/tests/helpers/testDatabaseLease.ts b/tests/helpers/testDatabaseLease.ts
index da79bfa2..e5109ee9 100644
--- a/tests/helpers/testDatabaseLease.ts
+++ b/tests/helpers/testDatabaseLease.ts
@@ -457,6 +457,16 @@ export const ensureLeasedConsent = async (
     // hitting the UNIQUE constraint. Autocommit is safe: we hold the
     // exclusive lease, so no live renamer can be mid-flight.
     await purgeOrphanedConsentRenames((query) => payload.db.drizzle.execute(query))
+    // Idempotent upsert: INSERT … ON CONFLICT (key) DO NOTHING eliminates the
+    // TOCTOU race between the find and the create — even if two ensures slip
+    // past the advisory lock under extreme load, the UNIQUE consent_key_idx
+    // guarantees exactly one row. The subsequent find always returns the
+    // committed row (created by this INSERT or a prior one).
+    await payload.db.drizzle.execute(sql`
+      INSERT INTO "consent" ("key", "text", "updated_at", "created_at")
+      VALUES (${consentKey}, ${fixtureConsentText}, now(), now())
+      ON CONFLICT ("key") DO NOTHING
+    `)
     const existing = await payload.find({
       collection: 'consent',
       where: { key: { equals: consentKey } },
@@ -464,16 +474,10 @@ export const ensureLeasedConsent = async (
       sort: 'id',
       depth: 0,
     })
-    if (existing.docs[0]) return existing.docs[0]
-
-    return payload.create({
-      collection: 'consent',
-      data: {
-        key: consentKey,
-        text: fixtureConsentText,
-      },
-      depth: 0,
-    })
+    if (!existing.docs[0]) {
+      throw new Error(`ensureLeasedConsent: consent key "${consentKey}" not found after upsert.`)
+    }
+    return existing.docs[0]
   })
 
 export const withLeasedConsent = async <Result>(
diff --git a/tests/int/campaignSuggestions.int.spec.ts b/tests/int/campaignSuggestions.int.spec.ts
index ba7a9abc..d634425f 100644
--- a/tests/int/campaignSuggestions.int.spec.ts
+++ b/tests/int/campaignSuggestions.int.spec.ts
@@ -276,9 +276,11 @@ describe('loadMunicipalitySuggestions (E11)', () => {
 
     // A quiet município cannot be staged — quietness means NO artifact-anchored
     // pattern fires — so claim through the allocator until one qualifies
-    // (measured: 205 of 435 with zeroed rows).
+    // (measured: 205 of 435 with zeroed rows → P(fail in 30) ≈ 0.53^30 ≈ 7e-9).
+    // 30 attempts keeps the flake probability negligible even under parallel load
+    // where the effective quiet rate may dip below the nominal 47%.
     let municipality: Municipality | null = null
-    for (let attempt = 0; attempt < 10; attempt += 1) {
+    for (let attempt = 0; attempt < 30; attempt += 1) {
       const candidate = await fixtures.getMunicipality()
       await normalizeMunicipality(candidate, { priority: 'alta' })
       fixtures.touchMunicipality(candidate.id)
@@ -289,7 +291,7 @@ describe('loadMunicipalitySuggestions (E11)', () => {
         break
       }
     }
-    if (!municipality) throw new Error('Nenhum município silencioso em 10 alocações.')
+    if (!municipality) throw new Error('Nenhum município silencioso em 30 alocações.')
 
     const author = await fixtures.createCampaignUser('coordinator')
     await fixtures.createMunicipalityUpdate({