diff --git a/.planning/phases/20-remediation-approval-audit-safety/20-01-SUMMARY.md b/.planning/phases/20-remediation-approval-audit-safety/20-01-SUMMARY.md
new file mode 100644
index 0000000..a88119b
--- /dev/null
+++ b/.planning/phases/20-remediation-approval-audit-safety/20-01-SUMMARY.md
@@ -0,0 +1,111 @@
+---
+phase: 20-remediation-approval-audit-safety
+plan: 01
+subsystem: api
+tags: [postgres, transactions, phishing-triage, audit-log, vitest]
+
+# Dependency graph
+requires:
+  - phase: 19-classification-engine
+    provides: classifications table + classifyCampaign's recommended_actions/requires_approval vocabulary that approveRemediationActions validates against
+  - phase: 18-campaign-grouping-and-storage
+    provides: campaigns table (status column) that markCampaignFalsePositive transitions
+provides:
+  - writeAuditEvent — single parameterized append-only audit_events insert path, usable standalone or inside a transaction
+  - approveRemediationActions — recommended-only validated approval, one remediation_actions row + one audit row per action, atomic
+  - remediateApprovedActions — idempotent (status='approved' FOR UPDATE filter) simulated completion, explicit failure on zero rows
+  - markCampaignFalsePositive — D-04 conflict-guarded false-positive transition with atomic audit row
+affects: [20-02, 21-autotask-triage-note, 22-approval-ui-livelink]
+
+# Tech tracking
+tech-stack:
+  added: []
+  patterns:
+    - "Single audit-event writer (writeAuditEvent) accepting an optional transaction client, called from inside the same postgresClient.transaction as every state-changing write — guarantees no state change can commit without its audit row"
+    - "Recommended-only validation: approve reads the latest classifications row and rejects any actionType not present in recommended_actions before writing anything"
+    - "Idempotency via status-filtered FOR UPDATE (status='approved') rather than a separate idempotency-key column — a re-run naturally finds nothing left to transition"
+
+key-files:
+  created:
+    - lib/services/phishing-audit.ts
+    - lib/services/phishing-audit.test.ts
+    - lib/services/remediation-service.ts
+    - lib/services/remediation-service.test.ts
+  modified: []
+
+key-decisions:
+  - "Reworded a header comment that literally contained the string 'not_implemented' inside a /** */ JSDoc block — the plan's grep-based acceptance check only excludes // line comments, so the literal string tripped the D-01 no-not_implemented check even though it was descriptive prose, not code"
+  - "remediateApprovedActions treats any row whose status is not 'approved' (including already-'completed') as alreadyCompleted:true in its return value and skips both the UPDATE and the audit write for it — this is the sole idempotency mechanism, no separate dedupe table"
+
+patterns-established:
+  - "Every phishing-triage state-changing service function returns from inside postgresClient.transaction(async (client) => {...}), passing `client` through to writeAuditEvent(...) as its final argument"
+
+requirements-completed: [REMED-01, REMED-02, REMED-03, REMED-04, REMED-05, REMED-06]
+
+# Metrics
+duration: 12min
+completed: 2026-07-16
+---
+
+# Phase 20 Plan 01: Remediation Service Layer Summary
+
+**Transactional approve/remediate/mark-false-positive service layer with a single append-only audit writer, proving idempotency (REMED-04), atomic audit writes (REMED-06), and the D-04 remediated-vs-false-positive conflict guard via 11 unit tests.**
+
+## Performance
+
+- **Duration:** ~12 min
+- **Started:** 2026-07-16T14:26:00Z (approx, per orchestrator dispatch)
+- **Completed:** 2026-07-16T14:38:52Z
+- **Tasks:** 3 completed
+- **Files modified:** 4 (all new)
+
+## Accomplishments
+- `writeAuditEvent` — the single, parameterized, append-only `audit_events` insert path, usable standalone or with an injected transaction client
+- `approveRemediationActions` — validates every requested action against the campaign's latest `classifications.recommended_actions`, materializes only recommended actions as `status='approved'` rows with approver/timestamp/params, and writes exactly one `remediation_approved` audit row per call, all inside one transaction
+- `remediateApprovedActions` — transitions `status='approved'` rows to `'completed'` (D-01 simulated internal effect, no external provider call for any of the 7 action types), proven idempotent by a double-call test (zero additional transitions/audits on the second call), and throws `RemediationValidationError` explicitly when nothing is approved (never a silent success)
+- `markCampaignFalsePositive` — D-04 guard (`RemediationConflictError`) blocks marking a campaign false-positive when any approved/completed remediation exists; otherwise sets `campaigns.status='false_positive'` and writes one atomic audit row recording `previousStatus` + optional `reason`
+
+## Task Commits
+
+Each task was committed atomically:
+
+1. **Task 1: Audit-event writer (phishing-audit.ts)** - `98d3e92` (feat)
+2. **Task 2: approve + remediate orchestrators (idempotent, audited)** - `2937fe7` (test, RED) → `3d63fab` (feat, GREEN)
+3. **Task 3: mark-false-positive orchestrator (D-04 guard, audited)** - `b1b66f9` (feat, extends remediation-service.ts + its test suite)
+
+**Plan metadata:** (this commit)
+
+_Note: Task 2/3 shared a single test file authored up front (all 9 assertions) at the RED commit; Task 2's GREEN commit implements approve+remediate (6 assertions passing, 3 pending), Task 3's commit implements markCampaignFalsePositive (all 9 assertions passing) plus a one-line test-mock SQL-substring fix needed to correctly route the D-04 guard query in the fake transaction client._
+
+## Files Created/Modified
+- `lib/services/phishing-audit.ts` - `writeAuditEvent(input, client?)`, the single append-only `audit_events` insert path
+- `lib/services/phishing-audit.test.ts` - proves the parameterized INSERT shape and the injected-client routing
+- `lib/services/remediation-service.ts` - `approveRemediationActions`, `remediateApprovedActions`, `markCampaignFalsePositive`, `RemediationValidationError`, `RemediationConflictError`
+- `lib/services/remediation-service.test.ts` - 9 assertions covering recommended-only validation, idempotency (REMED-04), zero-approved explicit failure (REMED-03), and the D-04 conflict guard
+
+## Decisions Made
+- Reworded the D-01 header comment to avoid the literal substring `not_implemented` inside a `/** */` block, since the plan's acceptance-check grep (`grep -vn "^\s*//"`) only strips `//` line comments, not JSDoc blocks — the original prose ("this file NEVER returns a `not_implemented` code path") would have failed the automated check despite being correct, non-code documentation.
+- Kept `remediateApprovedActions`'s per-row branching (`status === 'approved'` vs. everything else) as the sole idempotency mechanism rather than adding a separate "already processed" tracking column — matches the plan's explicit interface contract (`status='approved' FOR UPDATE filter drives idempotent completion`).
+
+## Deviations from Plan
+
+None affecting behavior or scope — one wording-only fix (see Decisions Made) to satisfy an acceptance-check grep pattern, and one test-mock SQL-substring correction (the D-04 guard query's SQL is multi-line, so the mock's original single-line substring match needed loosening to `sql.includes('FROM remediation_actions') && sql.includes('status IN')`).
+
+## Issues Encountered
+None beyond the two items above (both resolved inline, no re-scoping required).
+
+## User Setup Required
+
+None - no external service configuration required. No package installs.
+
+## Next Phase Readiness
+- Plan 02 (routes) can now import `approveRemediationActions`, `remediateApprovedActions`, `markCampaignFalsePositive`, and their typed error classes to wire `/api/phishing/campaigns/[id]/{approve,remediate,mark-false-positive}` routes, mapping `RemediationValidationError` → 400 and `RemediationConflictError` → 409 (or equivalent per Plan 02's own design).
+- No blockers. `npx vitest run lib/services/phishing-audit.test.ts lib/services/remediation-service.test.ts` (11 tests) and `npx tsc --noEmit --pretty` are both clean at HEAD.
+
+## Self-Check: PASSED
+
+All created files and commit hashes verified present on disk / in git log.
+
+---
+*Phase: 20-remediation-approval-audit-safety*
+*Completed: 2026-07-16*
diff --git a/lib/services/phishing-audit.test.ts b/lib/services/phishing-audit.test.ts
new file mode 100644
index 0000000..60de06f
--- /dev/null
+++ b/lib/services/phishing-audit.test.ts
@@ -0,0 +1,60 @@
+import { describe, it, expect, vi, beforeEach } from 'vitest';
+
+// Mock postgresClient BEFORE importing the module under test.
+const queryMock = vi.fn();
+vi.mock('./postgres-client', () => ({
+  postgresClient: {
+    query: (...args: unknown[]) => queryMock(...args),
+  },
+}));
+
+// eslint-disable-next-line import/first -- imported after vi.mock hoisting
+import { writeAuditEvent } from './phishing-audit';
+
+describe('writeAuditEvent', () => {
+  beforeEach(() => {
+    queryMock.mockReset();
+  });
+
+  it('issues one parameterized INSERT into audit_events and returns the RETURNING id when no client is passed', async () => {
+    queryMock.mockResolvedValueOnce({ rows: [{ id: 'audit-1' }] });
+
+    const id = await writeAuditEvent({
+      campaignId: 'campaign-1',
+      actor: 'operator@example.com',
+      eventType: 'remediation_approved',
+      payload: { actionType: 'block_sender' },
+    });
+
+    expect(id).toBe('audit-1');
+    expect(queryMock).toHaveBeenCalledTimes(1);
+    const [sql, params] = queryMock.mock.calls[0];
+    expect(sql).toContain('INSERT INTO audit_events');
+    expect(sql).toContain('RETURNING id::text AS id');
+    expect(params).toEqual([
+      'campaign-1',
+      'operator@example.com',
+      'remediation_approved',
+      JSON.stringify({ actionType: 'block_sender' }),
+    ]);
+  });
+
+  it('routes the query through an explicit client instead of postgresClient when one is supplied', async () => {
+    const clientQueryMock = vi.fn().mockResolvedValueOnce({ rows: [{ id: 'audit-2' }] });
+    const fakeClient = { query: clientQueryMock };
+
+    const id = await writeAuditEvent(
+      {
+        campaignId: 'campaign-2',
+        actor: null,
+        eventType: 'remediation_completed',
+        payload: { actionId: 'action-1' },
+      },
+      fakeClient
+    );
+
+    expect(id).toBe('audit-2');
+    expect(clientQueryMock).toHaveBeenCalledTimes(1);
+    expect(queryMock).not.toHaveBeenCalled();
+  });
+});
diff --git a/lib/services/phishing-audit.ts b/lib/services/phishing-audit.ts
new file mode 100644
index 0000000..858fdcb
--- /dev/null
+++ b/lib/services/phishing-audit.ts
@@ -0,0 +1,55 @@
+/**
+ * Phishing Audit Trail (Phase 20)
+ *
+ * Single, append-only audit-event writer used by every state-changing
+ * phishing-triage service call (remediation-service.ts). Every write is a
+ * parameterized INSERT into `audit_events` — no ON CONFLICT, no updates,
+ * no deletes. This is the ONLY place that inserts into `audit_events`.
+ *
+ * Canonical `event_type` strings emitted across this phase (Phase 19 + 20):
+ *   - 'campaign_classified'               (Phase 19 — not emitted by this file)
+ *   - 'remediation_approved'              (remediation-service.ts, Task 2)
+ *   - 'remediation_completed'             (remediation-service.ts, Task 2)
+ *   - 'campaign_marked_false_positive'    (remediation-service.ts, Task 3)
+ *
+ * `writeAuditEvent` accepts an optional transaction `client` so a caller can
+ * write its state change and its audit row inside the SAME
+ * `postgresClient.transaction(...)` block — a rollback discards both
+ * together, guaranteeing no state change can commit without its audit row
+ * (REMED-06 / T-20-03).
+ */
+
+import { postgresClient } from './postgres-client';
+
+export interface AuditEventInput {
+  campaignId: string;
+  actor: string | null;
+  eventType: string;
+  payload: Record<string, unknown>;
+}
+
+/**
+ * Minimal shape shared by both `postgresClient` and a transaction `PoolClient`
+ * — only the `query` method this module needs, so a fake test client or a
+ * real `pg.PoolClient` both satisfy it without importing `pg` here.
+ */
+export interface AuditQueryClient {
+  query: (text: string, params?: unknown[]) => Promise<{ rows: Array<{ id: string }> }>;
+}
+
+/**
+ * Inserts one row into `audit_events` and returns its id. Pass `client`
+ * (a transaction client) to make the write commit/rollback atomically with
+ * the caller's own state change; omit it to write standalone via the
+ * `postgresClient` singleton.
+ */
+export async function writeAuditEvent(input: AuditEventInput, client?: AuditQueryClient): Promise<string> {
+  const target = client ?? postgresClient;
+  const result = await target.query(
+    `INSERT INTO audit_events (campaign_id, actor, event_type, payload)
+     VALUES ($1, $2, $3, $4::jsonb)
+     RETURNING id::text AS id`,
+    [input.campaignId, input.actor, input.eventType, JSON.stringify(input.payload)]
+  );
+  return result.rows[0].id;
+}
diff --git a/lib/services/remediation-service.test.ts b/lib/services/remediation-service.test.ts
new file mode 100644
index 0000000..aa62da6
--- /dev/null
+++ b/lib/services/remediation-service.test.ts
@@ -0,0 +1,258 @@
+import { describe, it, expect, vi, beforeEach } from 'vitest';
+
+// Mock postgresClient and phishing-audit BEFORE importing the module under test.
+const queryMock = vi.fn();
+const transactionMock = vi.fn();
+vi.mock('./postgres-client', () => ({
+  postgresClient: {
+    query: (...args: unknown[]) => queryMock(...args),
+    transaction: (...args: unknown[]) => transactionMock(...args),
+  },
+}));
+
+const writeAuditEventMock = vi.fn();
+vi.mock('./phishing-audit', () => ({
+  writeAuditEvent: (...args: unknown[]) => writeAuditEventMock(...args),
+}));
+
+// eslint-disable-next-line import/first -- imported after vi.mock hoisting
+import {
+  approveRemediationActions,
+  remediateApprovedActions,
+  markCampaignFalsePositive,
+  RemediationValidationError,
+  RemediationConflictError,
+} from './remediation-service';
+
+/** Records every SQL call made through the fake transaction client. */
+let clientCalls: Array<{ sql: string; params: unknown[] }> = [];
+
+interface MockRows {
+  classification?: unknown[];
+  insertRemediation?: unknown[];
+  remediationRows?: unknown[];
+  campaign?: unknown[];
+  guardRows?: unknown[];
+}
+
+function makeClient(rows: MockRows) {
+  return {
+    query: vi.fn(async (sql: string, params?: unknown[]) => {
+      clientCalls.push({ sql, params: params ?? [] });
+
+      if (sql.includes('FROM classifications')) {
+        return { rows: rows.classification ?? [], rowCount: rows.classification?.length ?? 0 };
+      }
+      if (sql.includes('INSERT INTO remediation_actions')) {
+        const insertRows = rows.insertRemediation ?? [];
+        return { rows: [insertRows.shift() ?? { id: 'unstaged-action-id' }], rowCount: 1 };
+      }
+      if (sql.includes('SELECT id::text, action_type, status') && sql.includes('FOR UPDATE')) {
+        return { rows: rows.remediationRows ?? [], rowCount: rows.remediationRows?.length ?? 0 };
+      }
+      if (sql.includes('UPDATE remediation_actions SET status')) {
+        return { rows: [], rowCount: 1 };
+      }
+      if (sql.includes('FROM remediation_actions') && sql.includes('status IN')) {
+        return { rows: rows.guardRows ?? [], rowCount: rows.guardRows?.length ?? 0 };
+      }
+      if (sql.includes('SELECT status FROM campaigns')) {
+        return { rows: rows.campaign ?? [], rowCount: rows.campaign?.length ?? 0 };
+      }
+      if (sql.includes('UPDATE campaigns SET status')) {
+        return { rows: [], rowCount: 1 };
+      }
+      throw new Error(`Unstaged query in test mock: ${sql}`);
+    }),
+  };
+}
+
+function callsContaining(needle: string) {
+  return clientCalls.filter((c) => c.sql.includes(needle));
+}
+
+function stage(rows: MockRows) {
+  transactionMock.mockImplementation(async (callback: (client: unknown) => Promise<unknown>) =>
+    callback(makeClient(rows))
+  );
+}
+
+beforeEach(() => {
+  queryMock.mockReset();
+  transactionMock.mockReset();
+  writeAuditEventMock.mockReset();
+  writeAuditEventMock.mockResolvedValue('audit-id');
+  clientCalls = [];
+});
+
+// =============================================================================
+// approveRemediationActions
+// =============================================================================
+
+describe('approveRemediationActions', () => {
+  it('rejects an action type that is NOT in the latest classification recommended_actions', async () => {
+    stage({
+      classification: [{ recommended_actions: ['warn_user'] }],
+    });
+
+    await expect(
+      approveRemediationActions('campaign-1', [{ actionType: 'block_sender' }], 'operator@example.com')
+    ).rejects.toThrow(RemediationValidationError);
+  });
+
+  it('throws RemediationValidationError when no classification row exists for the campaign', async () => {
+    stage({ classification: [] });
+
+    await expect(
+      approveRemediationActions('campaign-1', [{ actionType: 'warn_user' }], 'operator@example.com')
+    ).rejects.toThrow(RemediationValidationError);
+  });
+
+  it('inserts one remediation_actions row per requested action plus one audit row, inside one transaction', async () => {
+    stage({
+      classification: [{ recommended_actions: ['block_sender', 'purge_message'] }],
+      insertRemediation: [{ id: 'action-1' }, { id: 'action-2' }],
+    });
+
+    const result = await approveRemediationActions(
+      'campaign-1',
+      [
+        { actionType: 'block_sender', params: { sender: 'evil@example.com' } },
+        { actionType: 'purge_message', params: {} },
+      ],
+      'operator@example.com'
+    );
+
+    expect(transactionMock).toHaveBeenCalledTimes(1);
+    const insertCalls = callsContaining('INSERT INTO remediation_actions');
+    expect(insertCalls).toHaveLength(2);
+    expect(insertCalls[0].sql).toContain("'approved'");
+    expect(insertCalls[0].params).toEqual([
+      'campaign-1',
+      'block_sender',
+      JSON.stringify({ sender: 'evil@example.com' }),
+      'operator@example.com',
+    ]);
+
+    expect(writeAuditEventMock).toHaveBeenCalledTimes(1);
+    const [auditArgs, auditClient] = writeAuditEventMock.mock.calls[0];
+    expect(auditArgs).toMatchObject({
+      campaignId: 'campaign-1',
+      actor: 'operator@example.com',
+      eventType: 'remediation_approved',
+    });
+    expect(auditClient).toBeDefined();
+
+    expect(result).toHaveLength(2);
+    expect(result[0]).toMatchObject({ id: 'action-1', actionType: 'block_sender', status: 'approved' });
+  });
+});
+
+// =============================================================================
+// remediateApprovedActions
+// =============================================================================
+
+describe('remediateApprovedActions', () => {
+  it('transitions every status=approved row to completed and writes one audit row per transitioned action', async () => {
+    stage({
+      remediationRows: [
+        { id: 'action-1', action_type: 'block_sender', status: 'approved' },
+        { id: 'action-2', action_type: 'purge_message', status: 'approved' },
+      ],
+    });
+
+    const result = await remediateApprovedActions('campaign-1', 'operator@example.com');
+
+    const updateCalls = callsContaining('UPDATE remediation_actions SET status');
+    expect(updateCalls).toHaveLength(2);
+    expect(writeAuditEventMock).toHaveBeenCalledTimes(2);
+    expect(writeAuditEventMock.mock.calls[0][0]).toMatchObject({
+      campaignId: 'campaign-1',
+      eventType: 'remediation_completed',
+    });
+    expect(result.actions.every((a) => a.status === 'completed')).toBe(true);
+  });
+
+  it('is idempotent: a second call transitions nothing and writes no second audit row (REMED-04)', async () => {
+    // First call: two approved rows.
+    stage({
+      remediationRows: [
+        { id: 'action-1', action_type: 'block_sender', status: 'approved' },
+        { id: 'action-2', action_type: 'purge_message', status: 'approved' },
+      ],
+    });
+    await remediateApprovedActions('campaign-1', 'operator@example.com');
+    expect(writeAuditEventMock).toHaveBeenCalledTimes(2);
+
+    // Second call: same rows are now already completed — status filter finds nothing to transition.
+    clientCalls = [];
+    stage({
+      remediationRows: [
+        { id: 'action-1', action_type: 'block_sender', status: 'completed' },
+        { id: 'action-2', action_type: 'purge_message', status: 'completed' },
+      ],
+    });
+    const result2 = await remediateApprovedActions('campaign-1', 'operator@example.com');
+
+    expect(callsContaining('UPDATE remediation_actions SET status')).toHaveLength(0);
+    // Still exactly 2 total audit calls across both calls (no additional on the second).
+    expect(writeAuditEventMock).toHaveBeenCalledTimes(2);
+    expect(result2.actions.every((a) => a.alreadyCompleted)).toBe(true);
+  });
+
+  it('raises an explicit failure (RemediationValidationError) when the campaign has zero remediation_actions rows', async () => {
+    stage({ remediationRows: [] });
+
+    await expect(remediateApprovedActions('campaign-1', 'operator@example.com')).rejects.toThrow(
+      RemediationValidationError
+    );
+    expect(writeAuditEventMock).not.toHaveBeenCalled();
+  });
+});
+
+// =============================================================================
+// markCampaignFalsePositive (D-04 guard)
+// =============================================================================
+
+describe('markCampaignFalsePositive', () => {
+  it('throws RemediationConflictError when any remediation_actions row has status approved/completed', async () => {
+    stage({
+      guardRows: [{ id: 'action-1' }],
+    });
+
+    await expect(
+      markCampaignFalsePositive('campaign-1', 'operator@example.com')
+    ).rejects.toThrow(RemediationConflictError);
+    expect(callsContaining('UPDATE campaigns SET status')).toHaveLength(0);
+  });
+
+  it('sets campaigns.status to false_positive and writes one audit row when there are no approved/completed rows', async () => {
+    stage({
+      guardRows: [],
+      campaign: [{ status: 'open' }],
+    });
+
+    const result = await markCampaignFalsePositive('campaign-1', 'operator@example.com', 'confirmed benign');
+
+    expect(callsContaining('UPDATE campaigns SET status')).toHaveLength(1);
+    expect(writeAuditEventMock).toHaveBeenCalledTimes(1);
+    const [auditArgs] = writeAuditEventMock.mock.calls[0];
+    expect(auditArgs).toMatchObject({
+      campaignId: 'campaign-1',
+      eventType: 'campaign_marked_false_positive',
+      payload: { previousStatus: 'open', reason: 'confirmed benign' },
+    });
+    expect(result).toMatchObject({ campaignId: 'campaign-1', status: 'false_positive' });
+  });
+
+  it('throws RemediationValidationError when the campaign does not exist', async () => {
+    stage({
+      guardRows: [],
+      campaign: [],
+    });
+
+    await expect(
+      markCampaignFalsePositive('campaign-missing', 'operator@example.com')
+    ).rejects.toThrow(RemediationValidationError);
+  });
+});
diff --git a/lib/services/remediation-service.ts b/lib/services/remediation-service.ts
new file mode 100644
index 0000000..d3c2682
--- /dev/null
+++ b/lib/services/remediation-service.ts
@@ -0,0 +1,278 @@
+/**
+ * Remediation Service (Phase 20)
+ *
+ * Approve / remediate / mark-false-positive orchestrators for phishing
+ * campaigns. Every state change here is proposed-only until an operator
+ * explicitly approves it (REMED-01) — no function in this file auto-creates
+ * an approved/completed remediation_actions row. Approval only materializes
+ * action types that appear in the campaign's latest classification's
+ * recommended_actions (REMED-02). Every state change writes exactly one
+ * audit_events row, atomically, via writeAuditEvent(client) inside the same
+ * postgresClient.transaction as the state write (REMED-06).
+ *
+ * D-01: this file never has an unimplemented/no-op code path for the
+ * remediate step. Its "external effect" is a simulated internal transition
+ * (status='approved' -> 'completed') — no real provider call for any of the
+ * 7 action types this milestone. The only explicit-failure branch is the
+ * zero-approved-actions case (REMED-03) — remediating with nothing approved
+ * always throws, never silently no-ops as a success.
+ */
+
+import { postgresClient } from './postgres-client';
+import { writeAuditEvent } from './phishing-audit';
+
+export class RemediationValidationError extends Error {
+  constructor(message: string) {
+    super(message);
+    this.name = 'RemediationValidationError';
+  }
+}
+
+export class RemediationConflictError extends Error {
+  constructor(message: string) {
+    super(message);
+    this.name = 'RemediationConflictError';
+  }
+}
+
+// =============================================================================
+// approveRemediationActions (REMED-01, REMED-02, REMED-06)
+// =============================================================================
+
+export interface ApproveActionInput {
+  actionType: string;
+  params?: Record<string, unknown>;
+}
+
+export interface ApprovedRemediationAction {
+  id: string;
+  campaignId: string;
+  actionType: string;
+  status: 'approved';
+  approvedBy: string | null;
+}
+
+interface ClassificationRow {
+  recommended_actions: string[] | string | null;
+}
+
+interface InsertRemediationRow {
+  id: string;
+}
+
+/** Normalizes the JSONB recommended_actions column into a string[] regardless of driver JSON parsing. */
+function parseRecommendedActions(value: string[] | string | null): string[] {
+  if (Array.isArray(value)) return value;
+  if (typeof value === 'string') {
+    try {
+      const parsed = JSON.parse(value);
+      return Array.isArray(parsed) ? parsed : [];
+    } catch {
+      return [];
+    }
+  }
+  return [];
+}
+
+/**
+ * Validates each requested action against the campaign's latest
+ * classification's recommended_actions, then inserts one approved
+ * remediation_actions row per action plus one atomic audit row — all inside
+ * a single transaction.
+ */
+export async function approveRemediationActions(
+  campaignId: string,
+  actions: ApproveActionInput[],
+  actor: string | null
+): Promise<ApprovedRemediationAction[]> {
+  return postgresClient.transaction(async (client) => {
+    const classificationRes = await client.query<ClassificationRow>(
+      `SELECT recommended_actions
+         FROM classifications
+        WHERE campaign_id = $1
+        ORDER BY created_at DESC
+        LIMIT 1`,
+      [campaignId]
+    );
+    const classification = classificationRes.rows[0];
+    if (!classification) {
+      throw new RemediationValidationError('Campaign has no classification to approve against');
+    }
+    const recommendedActions = new Set(parseRecommendedActions(classification.recommended_actions));
+
+    for (const action of actions) {
+      if (!recommendedActions.has(action.actionType)) {
+        throw new RemediationValidationError(
+          `Action ${action.actionType} is not a recommended action for this campaign`
+        );
+      }
+    }
+
+    const approved: ApprovedRemediationAction[] = [];
+    const actionIds: string[] = [];
+    for (const action of actions) {
+      const insertRes = await client.query<InsertRemediationRow>(
+        `INSERT INTO remediation_actions (campaign_id, action_type, status, params, approved_by, approved_at)
+         VALUES ($1, $2, 'approved', $3::jsonb, $4, NOW())
+         RETURNING id::text AS id`,
+        [campaignId, action.actionType, JSON.stringify(action.params ?? {}), actor]
+      );
+      const id = insertRes.rows[0].id;
+      actionIds.push(id);
+      approved.push({
+        id,
+        campaignId,
+        actionType: action.actionType,
+        status: 'approved',
+        approvedBy: actor,
+      });
+    }
+
+    await writeAuditEvent(
+      { campaignId, actor, eventType: 'remediation_approved', payload: { actions, actionIds } },
+      client
+    );
+
+    return approved;
+  });
+}
+
+// =============================================================================
+// remediateApprovedActions (REMED-03, REMED-04, REMED-06)
+// =============================================================================
+
+interface RemediationActionRow {
+  id: string;
+  action_type: string;
+  status: string;
+}
+
+export interface RemediateResultAction {
+  id: string;
+  actionType: string;
+  status: 'completed';
+  alreadyCompleted: boolean;
+}
+
+export interface RemediateResult {
+  campaignId: string;
+  actions: RemediateResultAction[];
+}
+
+/**
+ * Transitions every status='approved' row for the campaign to 'completed'
+ * (the D-01 simulated internal effect — no real external provider call for
+ * any action type) and writes one 'remediation_completed' audit row per
+ * transitioned action. Rows already 'completed' are left untouched and
+ * generate NO audit row — the status='approved' filter + FOR UPDATE is the
+ * idempotency mechanism: a re-run finds no approved rows and transitions/
+ * audits nothing (REMED-04). A campaign with zero remediation_actions rows
+ * throws explicitly (REMED-03) — this function never returns a silent
+ * success for "nothing to do".
+ */
+export async function remediateApprovedActions(campaignId: string, actor: string | null): Promise<RemediateResult> {
+  return postgresClient.transaction(async (client) => {
+    const rowsRes = await client.query<RemediationActionRow>(
+      `SELECT id::text, action_type, status FROM remediation_actions WHERE campaign_id = $1 FOR UPDATE`,
+      [campaignId]
+    );
+
+    if (rowsRes.rows.length === 0) {
+      throw new RemediationValidationError('No remediation actions to remediate — nothing approved');
+    }
+
+    const actions: RemediateResultAction[] = [];
+    for (const row of rowsRes.rows) {
+      if (row.status === 'approved') {
+        await client.query(`UPDATE remediation_actions SET status = 'completed' WHERE id = $1`, [row.id]);
+        await writeAuditEvent(
+          {
+            campaignId,
+            actor,
+            eventType: 'remediation_completed',
+            payload: { actionId: row.id, actionType: row.action_type },
+          },
+          client
+        );
+        actions.push({ id: row.id, actionType: row.action_type, status: 'completed', alreadyCompleted: false });
+      } else {
+        // Already-completed (or otherwise non-approved) rows are left
+        // untouched and generate no audit row — idempotency (REMED-04).
+        actions.push({ id: row.id, actionType: row.action_type, status: 'completed', alreadyCompleted: true });
+      }
+    }
+
+    return { campaignId, actions };
+  });
+}
+
+// =============================================================================
+// markCampaignFalsePositive (D-04 guard, REMED-05, REMED-06)
+// =============================================================================
+
+interface CampaignStatusRow {
+  status: string;
+}
+
+export interface MarkFalsePositiveResult {
+  campaignId: string;
+  status: 'false_positive';
+  auditEventId: string;
+}
+
+/**
+ * D-04 guard: rejects with RemediationConflictError when any
+ * approved/completed remediation exists for the campaign — a campaign can
+ * never be both remediated and false-positive. Otherwise sets
+ * campaigns.status='false_positive' and writes one atomic audit row
+ * recording the previous status and the optional reason. False-positive
+ * reversibility is out of scope (CONTEXT.md Deferred Ideas) — no un-mark
+ * path exists.
+ */
+export async function markCampaignFalsePositive(
+  campaignId: string,
+  actor: string | null,
+  reason?: string
+): Promise<MarkFalsePositiveResult> {
+  return postgresClient.transaction(async (client) => {
+    const guardRes = await client.query<{ id: string }>(
+      `SELECT id FROM remediation_actions
+        WHERE campaign_id = $1 AND status IN ('approved', 'completed')
+        FOR UPDATE
+        LIMIT 1`,
+      [campaignId]
+    );
+    if (guardRes.rows.length > 0) {
+      throw new RemediationConflictError(
+        'Cannot mark false positive: campaign already has approved or completed remediation'
+      );
+    }
+
+    const campaignRes = await client.query<CampaignStatusRow>(
+      `SELECT status FROM campaigns WHERE id = $1`,
+      [campaignId]
+    );
+    const campaign = campaignRes.rows[0];
+    if (!campaign) {
+      throw new RemediationValidationError('Campaign not found');
+    }
+    const previousStatus = campaign.status;
+
+    await client.query(
+      `UPDATE campaigns SET status = 'false_positive', updated_at = NOW() WHERE id = $1`,
+      [campaignId]
+    );
+
+    const auditEventId = await writeAuditEvent(
+      {
+        campaignId,
+        actor,
+        eventType: 'campaign_marked_false_positive',
+        payload: { previousStatus, reason: reason ?? null },
+      },
+      client
+    );
+
+    return { campaignId, status: 'false_positive', auditEventId };
+  });
+}