diff --git a/src/lib/server/stock-quantities-service.test.ts b/src/lib/server/stock-quantities-service.test.ts
index b9b26ac..26f0faa 100644
--- a/src/lib/server/stock-quantities-service.test.ts
+++ b/src/lib/server/stock-quantities-service.test.ts
@@ -326,4 +326,73 @@ describe("updateStockItemsQuantities — multi-row batch", () => {
       change_qty: 5,
     });
   });
-});
\ No newline at end of file
+});
+
+describe("updateStockItemsQuantities — negative quantities", () => {
+  it("rejects a negative currentQty by default", async () => {
+    const { pb } = stubPb({ before: { id: "abcdefghijklmno", current_qty: 5 } });
+    const res = await updateStockItemsQuantities({
+      pb: pb as never,
+      updates: [{ id: "abcdefghijklmno", currentQty: -1 }],
+      actor: { id: "u1", name: "Dave" },
+    } as UpdateStockItemsQuantitiesInput);
+    const row = res.results[0];
+    expect(row.ok).toBe(false);
+    expect(row.ok === false && row.reason).toBe("validation_error");
+  });
+
+  it("accepts a negative currentQty when allowNegativeQty is set", async () => {
+    const { pb, ledgerCreates } = stubPb({
+      before: { id: "abcdefghijklmno", current_qty: 5 },
+    });
+    const res = await updateStockItemsQuantities({
+      pb: pb as never,
+      updates: [{ id: "abcdefghijklmno", currentQty: -3 }],
+      actor: { id: "u1", name: "Dave" },
+      allowNegativeQty: true,
+    } as UpdateStockItemsQuantitiesInput);
+    expect(res.summary.succeeded).toBe(1);
+    expect(ledgerCreates[0].change_qty).toBe(-8);
+    expect(ledgerCreates[0].notes).toBe("Dave edited qty 5 → -3 via Giellie");
+  });
+
+  it("keeps minQty floored at zero even with allowNegativeQty", async () => {
+    const { pb } = stubPb({ before: { id: "abcdefghijklmno", current_qty: 5 } });
+    const res = await updateStockItemsQuantities({
+      pb: pb as never,
+      updates: [{ id: "abcdefghijklmno", minQty: -1 }],
+      actor: { id: "u1", name: "Dave" },
+      allowNegativeQty: true,
+    } as UpdateStockItemsQuantitiesInput);
+    const row = res.results[0];
+    expect(row.ok).toBe(false);
+    expect(row.ok === false && row.reason).toBe("validation_error");
+  });
+});
+
+describe("updateStockItemsQuantities — ledger note context", () => {
+  it("defaults the note to the /stock page", async () => {
+    const { pb, ledgerCreates } = stubPb({
+      before: { id: "abcdefghijklmno", current_qty: 5 },
+    });
+    await updateStockItemsQuantities({
+      pb: pb as never,
+      updates: [{ id: "abcdefghijklmno", currentQty: 9 }],
+      actor: { id: "u1", name: "Dave" },
+    } as UpdateStockItemsQuantitiesInput);
+    expect(ledgerCreates[0].notes).toBe("Dave edited qty 5 → 9 from /stock");
+  });
+
+  it("uses the caller's context when given one", async () => {
+    const { pb, ledgerCreates } = stubPb({
+      before: { id: "abcdefghijklmno", current_qty: 5 },
+    });
+    await updateStockItemsQuantities({
+      pb: pb as never,
+      updates: [{ id: "abcdefghijklmno", currentQty: 9 }],
+      actor: { id: "u1", name: "Dave" },
+      noteContext: "via Giellie",
+    } as UpdateStockItemsQuantitiesInput);
+    expect(ledgerCreates[0].notes).toBe("Dave edited qty 5 → 9 via Giellie");
+  });
+});
diff --git a/src/lib/server/stock-quantities-service.ts b/src/lib/server/stock-quantities-service.ts
index b80044e..a8cf136 100644
--- a/src/lib/server/stock-quantities-service.ts
+++ b/src/lib/server/stock-quantities-service.ts
@@ -11,6 +11,12 @@ import type { StockItem } from "@/lib/types";
  * trail stays honest. `min_qty` and `target_qty` are simple
  * patch-as-you-go fields — no ledger row.
  *
+ * Two callers share it: the /stock page (which keeps a
+ * non-negative floor — the operator types a physical count there) and
+ * the Giellie agent (which may write an absolute count below zero,
+ * because the till oversells on purpose). The agent opts in with
+ * `allowNegativeQty`; the page never does.
+ *
  * Why a separate service instead of folding into
  * `updateStockItemsPricing`?
  *
@@ -46,6 +52,19 @@ export type UpdateStockItemsQuantitiesInput = {
   pb: StockItemsPb;
   updates: StockQuantityUpdate[];
   actor: { id: string; name: string };
+  /**
+   * When true, `currentQty` may be negative. The /stock UI keeps its
+   * non-negative floor — the operator types a physical count there. The
+   * agent needs to write an absolute count that can legitimately sit
+   * below zero, because the till oversells on purpose.
+   */
+  allowNegativeQty?: boolean;
+  /**
+   * Where the edit came from, appended to the ledger note. Defaults to
+   * "from /stock" for the /stock page, and to "via Giellie" for an
+   * agent write (one that sets `allowNegativeQty`).
+   */
+  noteContext?: string;
 };
 
 export type StockItemsPb = {
@@ -97,12 +116,21 @@ const PATCHABLE_KEYS = ["currentQty", "minQty", "targetQty"] as const;
  * `Math.trunc` decision in `stock/items/[id]/adjust/route.ts`. If
  * a future caller legitimately needs fractional (e.g. metres of
  * cable) they can drop the trunc and the test that pins it.
+ *
+ * `allowNegative` lifts the floor for that one call only — the agent
+ * writes an absolute count that can legitimately sit below zero,
+ * because the till oversells on purpose. `min_qty` and `target_qty`
+ * stay floored at zero regardless.
  */
-function coerceNonNegativeInt(
+function coerceQty(
   key: string,
   value: unknown,
+  allowNegative: boolean,
 ): number {
-  if (typeof value !== "number" || !Number.isFinite(value) || value < 0) {
+  if (typeof value !== "number" || !Number.isFinite(value)) {
+    throw new Error(`${key} must be a finite number`);
+  }
+  if (!allowNegative && value < 0) {
     throw new Error(`${key} must be a finite number >= 0`);
   }
   return Math.trunc(value);
@@ -124,6 +152,12 @@ export async function updateStockItemsQuantities(
 ): Promise<UpdateStockItemsQuantitiesResult> {
   const results: UpdateStockItemsQuantitiesResultRow[] = [];
 
+  // Where the edit came from, for the ledger note. The /stock page is
+  // the default; `allowNegativeQty` is the agent-only opt-in, so an
+  // agent write that does not name its own context still reads as one.
+  const noteContext =
+    input.noteContext ?? (input.allowNegativeQty ? "via Giellie" : "from /stock");
+
   for (const update of input.updates) {
     // 1. Whitelist + type validation. Reject the row on any
     //    forbidden / non-finite / negative field — partial patches
@@ -148,7 +182,11 @@ export async function updateStockItemsQuantities(
       const value = (update as Record<string, unknown>)[key];
       if (key !== "id" && value !== undefined) {
         try {
-          coerceNonNegativeInt(key, value);
+          coerceQty(
+            key,
+            value,
+            key === "currentQty" && input.allowNegativeQty === true,
+          );
         } catch (err) {
           results.push({
             id: update.id,
@@ -221,7 +259,7 @@ export async function updateStockItemsQuantities(
           change_qty: delta,
           reason: "adjustment",
           reference_type: "manual",
-          notes: `${input.actor.name} edited qty ${beforeCurrent} → ${requestedCurrent} from /stock`,
+          notes: `${input.actor.name} edited qty ${beforeCurrent} → ${requestedCurrent} ${noteContext}`,
           created_by: input.actor.id,
         });
         ledgerId = (created as { id: string }).id;