diff --git a/packages/loopover-miner/lib/governor-ledger.js b/packages/loopover-miner/lib/governor-ledger.js
index 4b5ecd30b6..fd7570b2a3 100644
--- a/packages/loopover-miner/lib/governor-ledger.js
+++ b/packages/loopover-miner/lib/governor-ledger.js
@@ -89,6 +89,18 @@ function rowToDecision(row) {
   };
 }
 
+// v1 -> v2 (#4939/#6597): additive tenant-scoping column, a prerequisite for any hosted, multi-tenant use of
+// this same store's logic. NULL for every row today -- self-host behavior is byte-identical, since nothing
+// reads or writes it yet. Same defensive column-presence guard as this file's sibling stores' own additive
+// migrations (e.g. event-ledger.js's addTenantIdColumn).
+function addTenantIdColumn(db) {
+  const hasTenantIdColumn = db
+    .prepare("PRAGMA table_info(governor_events)")
+    .all()
+    .some((column) => column.name === "tenant_id");
+  if (!hasTenantIdColumn) db.exec("ALTER TABLE governor_events ADD COLUMN tenant_id TEXT");
+}
+
 /**
  * Opens the append-only governor ledger, creating the table on first use. Rows are returned in ascending `id`
  * order (insertion order). (#2328)
@@ -109,8 +121,8 @@ export function initGovernorLedger(dbPath = resolveGovernorLedgerDbPath()) {
     )
   `);
   db.exec("CREATE INDEX IF NOT EXISTS idx_governor_events_repo ON governor_events (repo_full_name, id)");
-  // Schema-version convention (#4832): stamp the baseline and run any post-baseline migrations (none yet).
-  applySchemaMigrations(db, []);
+  // Schema-version convention (#4832): stamp the baseline and run any post-baseline migrations.
+  applySchemaMigrations(db, [addTenantIdColumn]);
   // Opt-in retention (#4834): prune aged/excess rows when an operator has enabled it; a no-op by default.
   pruneLedgerByRetention(db, GOVERNOR_LEDGER_RETENTION_SPEC, resolveLedgerRetentionPolicy(), Date.now());
 
diff --git a/packages/loopover-miner/lib/plan-store.js b/packages/loopover-miner/lib/plan-store.js
index 8d7a3be3fa..a289648d05 100644
--- a/packages/loopover-miner/lib/plan-store.js
+++ b/packages/loopover-miner/lib/plan-store.js
@@ -142,6 +142,18 @@ function rowToRecord(row) {
   return { planId: row.plan_id, plan, status: row.status, updatedAt: row.updated_at };
 }
 
+// v1 -> v2 (#4939/#6597): additive tenant-scoping column, a prerequisite for any hosted, multi-tenant use of
+// this same store's logic. NULL for every row today -- self-host behavior is byte-identical, since nothing
+// reads or writes it yet. Same defensive column-presence guard as this file's sibling stores' own additive
+// migrations (e.g. event-ledger.js's addTenantIdColumn).
+function addTenantIdColumn(db) {
+  const hasTenantIdColumn = db
+    .prepare("PRAGMA table_info(miner_plans)")
+    .all()
+    .some((column) => column.name === "tenant_id");
+  if (!hasTenantIdColumn) db.exec("ALTER TABLE miner_plans ADD COLUMN tenant_id TEXT");
+}
+
 /**
  * Opens the local plan store, creating the table on first use. `savePlan` is a single atomic INSERT…ON CONFLICT
  * upsert keyed by `plan_id`; the plan JSON is validated on save AND re-validated on load, so a corrupted row is
@@ -160,8 +172,8 @@ export function openPlanStore(dbPath = resolvePlanStoreDbPath()) {
       updated_at TEXT NOT NULL
     )
   `);
-  // Schema-version convention (#4832): stamp the baseline and run any post-baseline migrations (none yet).
-  applySchemaMigrations(db, []);
+  // Schema-version convention (#4832): stamp the baseline and run any post-baseline migrations.
+  applySchemaMigrations(db, [addTenantIdColumn]);
 
   const saveStatement = db.prepare(`
     INSERT INTO miner_plans (plan_id, plan_json, status, updated_at)
diff --git a/test/unit/miner-governor-ledger.test.ts b/test/unit/miner-governor-ledger.test.ts
index d4ec6db29b..299df09fb6 100644
--- a/test/unit/miner-governor-ledger.test.ts
+++ b/test/unit/miner-governor-ledger.test.ts
@@ -15,6 +15,7 @@ import {
   readGovernorEvents,
   resolveGovernorLedgerDbPath,
 } from "../../packages/loopover-miner/lib/governor-ledger.js";
+import { readSchemaVersion } from "../../packages/loopover-miner/lib/schema-version.js";
 
 const roots: string[] = [];
 const ledgers: Array<{ close(): void }> = [];
@@ -214,4 +215,76 @@ describe("loopover-miner governor ledger (#2328)", () => {
       else process.env.LOOPOVER_MINER_CONFIG_DIR = previousConfigDir;
     }
   });
+
+  describe("schema migrations (#6597)", () => {
+    it("v1 -> v2 (#4939/#6597): adds an additive tenant_id column, NULL for every pre-existing row -- self-host behavior byte-identical", () => {
+      const root = mkdtempSync(join(tmpdir(), "loopover-miner-governor-legacy-v1-"));
+      roots.push(root);
+      const dbPath = join(root, "legacy-v1.sqlite3");
+      const legacy = new DatabaseSync(dbPath);
+      legacy.exec(`
+        CREATE TABLE governor_events (
+          id INTEGER PRIMARY KEY AUTOINCREMENT,
+          ts TEXT NOT NULL,
+          event_type TEXT NOT NULL,
+          repo_full_name TEXT,
+          action_class TEXT NOT NULL,
+          decision TEXT NOT NULL,
+          reason TEXT NOT NULL,
+          payload_json TEXT NOT NULL
+        )
+      `);
+      legacy.exec("CREATE INDEX idx_governor_events_repo ON governor_events (repo_full_name, id)");
+      legacy.exec("PRAGMA user_version = 1");
+      legacy.exec(
+        "INSERT INTO governor_events (ts, event_type, repo_full_name, action_class, decision, reason, payload_json) VALUES ('2026-01-01T00:00:00.000Z', 'allowed', 'acme/widgets', 'analyze', 'allow', 'within budget', '{}')",
+      );
+      legacy.close();
+
+      const ledger = initGovernorLedger(dbPath);
+      ledgers.push(ledger);
+      expect(ledger.readGovernorEvents().map((event) => event.eventType)).toEqual(["allowed"]);
+      const readonly = new DatabaseSync(dbPath, { readOnly: true });
+      const columns = readonly.prepare("PRAGMA table_info(governor_events)").all() as Array<{ name: string }>;
+      expect(columns.map((column) => column.name)).toContain("tenant_id");
+      expect(readSchemaVersion(readonly)).toBe(2);
+      const row = readonly.prepare("SELECT tenant_id FROM governor_events WHERE id = 1").get() as { tenant_id: string | null };
+      expect(row.tenant_id).toBeNull();
+      readonly.close();
+    });
+
+    it("REGRESSION: a v1 file that (unusually) already carries tenant_id is not re-altered into a duplicate-column error", () => {
+      const root = mkdtempSync(join(tmpdir(), "loopover-miner-governor-legacy-partial-v2-"));
+      roots.push(root);
+      const dbPath = join(root, "legacy-partial-v2.sqlite3");
+      const legacy = new DatabaseSync(dbPath);
+      legacy.exec(`
+        CREATE TABLE governor_events (
+          id INTEGER PRIMARY KEY AUTOINCREMENT,
+          ts TEXT NOT NULL,
+          event_type TEXT NOT NULL,
+          repo_full_name TEXT,
+          action_class TEXT NOT NULL,
+          decision TEXT NOT NULL,
+          reason TEXT NOT NULL,
+          payload_json TEXT NOT NULL,
+          tenant_id TEXT
+        )
+      `);
+      legacy.exec("PRAGMA user_version = 1");
+      legacy.close();
+
+      expect(() => {
+        const ledger = initGovernorLedger(dbPath);
+        ledgers.push(ledger);
+      }).not.toThrow();
+    });
+
+    it("opening a fresh store reports user_version = 2 via readSchemaVersion", () => {
+      const ledger = tempLedger();
+      const readonly = new DatabaseSync(ledger.dbPath, { readOnly: true });
+      expect(readSchemaVersion(readonly)).toBe(2);
+      readonly.close();
+    });
+  });
 });
diff --git a/test/unit/miner-plan-store.test.ts b/test/unit/miner-plan-store.test.ts
index 6770cf987c..94b1076599 100644
--- a/test/unit/miner-plan-store.test.ts
+++ b/test/unit/miner-plan-store.test.ts
@@ -10,6 +10,7 @@ import {
   resolvePlanStoreDbPath,
 } from "../../packages/loopover-miner/lib/plan-store.js";
 import type { PlanDag } from "../../packages/loopover-miner/lib/plan-store.js";
+import { readSchemaVersion } from "../../packages/loopover-miner/lib/schema-version.js";
 
 const roots: string[] = [];
 const stores: Array<{ close(): void }> = [];
@@ -172,4 +173,65 @@ describe("loopover-miner plan store (#2318)", () => {
     expect(() => store.loadPlan("p1")).toThrow("corrupted_plan_row");
     expect(() => store.listPlans()).toThrow("corrupted_plan_row");
   });
+
+  describe("schema migrations (#6597)", () => {
+    it("v1 -> v2 (#4939/#6597): adds an additive tenant_id column, NULL for every pre-existing row -- self-host behavior byte-identical", () => {
+      const root = mkdtempSync(join(tmpdir(), "loopover-miner-plan-store-legacy-v1-"));
+      roots.push(root);
+      const dbPath = join(root, "legacy-v1.sqlite3");
+      const legacy = new DatabaseSync(dbPath);
+      legacy.exec(`
+        CREATE TABLE miner_plans (
+          plan_id TEXT PRIMARY KEY,
+          plan_json TEXT NOT NULL,
+          status TEXT NOT NULL CHECK (status IN ('pending', 'running', 'completed', 'failed')),
+          updated_at TEXT NOT NULL
+        )
+      `);
+      legacy.exec("PRAGMA user_version = 1");
+      legacy.prepare("INSERT INTO miner_plans (plan_id, plan_json, status, updated_at) VALUES (?, ?, ?, ?)").run("p1", JSON.stringify(PLAN), "running", "2026-01-01T00:00:00.000Z");
+      legacy.close();
+
+      const store = openPlanStore(dbPath);
+      stores.push(store);
+      expect(store.listPlans().map((record) => record.planId)).toEqual(["p1"]);
+      const readonly = new DatabaseSync(dbPath, { readOnly: true });
+      const columns = readonly.prepare("PRAGMA table_info(miner_plans)").all() as Array<{ name: string }>;
+      expect(columns.map((column) => column.name)).toContain("tenant_id");
+      expect(readSchemaVersion(readonly)).toBe(2);
+      const row = readonly.prepare("SELECT tenant_id FROM miner_plans WHERE plan_id = ?").get("p1") as { tenant_id: string | null };
+      expect(row.tenant_id).toBeNull();
+      readonly.close();
+    });
+
+    it("REGRESSION: a v1 file that (unusually) already carries tenant_id is not re-altered into a duplicate-column error", () => {
+      const root = mkdtempSync(join(tmpdir(), "loopover-miner-plan-store-legacy-partial-v2-"));
+      roots.push(root);
+      const dbPath = join(root, "legacy-partial-v2.sqlite3");
+      const legacy = new DatabaseSync(dbPath);
+      legacy.exec(`
+        CREATE TABLE miner_plans (
+          plan_id TEXT PRIMARY KEY,
+          plan_json TEXT NOT NULL,
+          status TEXT NOT NULL CHECK (status IN ('pending', 'running', 'completed', 'failed')),
+          updated_at TEXT NOT NULL,
+          tenant_id TEXT
+        )
+      `);
+      legacy.exec("PRAGMA user_version = 1");
+      legacy.close();
+
+      expect(() => {
+        const store = openPlanStore(dbPath);
+        stores.push(store);
+      }).not.toThrow();
+    });
+
+    it("opening a fresh store reports user_version = 2 via readSchemaVersion", () => {
+      const store = tempStore();
+      const readonly = new DatabaseSync(store.dbPath, { readOnly: true });
+      expect(readSchemaVersion(readonly)).toBe(2);
+      readonly.close();
+    });
+  });
 });