diff --git a/packages/gittensory-engine/src/discovery-soft-claim.ts b/packages/gittensory-engine/src/discovery-soft-claim.ts
new file mode 100644
index 0000000000..32736e3f0d
--- /dev/null
+++ b/packages/gittensory-engine/src/discovery-soft-claim.ts
@@ -0,0 +1,96 @@
+import { DISCOVERY_INDEX_CONTRACT_VERSION } from "./discovery-index-contract.js";
+
+// Soft-claim coordination request builder (#4302). The local soft-claim ledger (claim-ledger.js) is 100%
+// client-side — "never uploads, syncs, or phones home" — and duplicate-cluster adjudication
+// (isDuplicateClusterWinnerByClaim, #3355) only resolves collisions AFTER the fact, by observing which PR/comment
+// publicly landed first. This module closes that gap on the client side: a pure function that turns a local claim
+// record into the request payload a miner would send to the optional hosted discovery-index (the contract in
+// discovery-index-contract.ts, #4300) to softly announce/reserve an issue across the fleet BEFORE starting, so
+// collisions are reduced rather than only detected afterward.
+//
+// Scoped as a "request builder", not a network client: pure input→output, no HTTP (wiring the hosted plane's
+// client into the miner runtime is downstream of #4250 existing). It shares the discovery-index contract's posture:
+// metadata-only and public-safe by construction — the request is built by explicitly copying a fixed set of
+// known fields, never by spreading the input, so no unexpected/forbidden field can ride along.
+//
+// DECISION (the issue's open question — reject vs. release for non-active claims): a `released`/`expired` claim
+// produces an explicit `release` request variant rather than being rejected, so the fleet learns an issue is free
+// again; only an `active` claim produces a `claim` request.
+
+/** The three local claim-ledger statuses (claim-ledger.js `CLAIM_STATUSES`). */
+export type SoftClaimStatus = "active" | "released" | "expired";
+
+/** Outbound coordination actions: announce a claim, or announce that a prior claim is released. */
+export type SoftClaimAction = "claim" | "release";
+
+/** The local claim-ledger record shape (claim-ledger.js `rowToClaim`) this builder reads from. */
+export type SoftClaimRecord = {
+  repoFullName: string;
+  issueNumber: number;
+  claimedAt: string;
+  status: SoftClaimStatus;
+  note?: string | null;
+};
+
+/** Optional caller context. `instanceId` is an opaque, caller-anonymized fleet handle — NOT a wallet/hotkey or any
+ *  identity secret; it is copied through verbatim and never interpreted here. */
+export type SoftClaimRequestContext = {
+  instanceId?: string;
+};
+
+/** The public-safe soft-claim coordination request payload targeting the discovery-index contract. */
+export type SoftClaimRequest = {
+  contractVersion: number;
+  action: SoftClaimAction;
+  repoFullName: string;
+  issueNumber: number;
+  claimedAt: string;
+  note: string | null;
+  instanceId: string | null;
+};
+
+/** `active` announces a `claim`; `released`/`expired` announce a `release`. */
+export function softClaimActionForStatus(status: SoftClaimStatus): SoftClaimAction {
+  return status === "active" ? "claim" : "release";
+}
+
+/** `owner/repo` with exactly one slash and non-empty halves; anything else → null (mirrors the discovery-index
+ *  contract / claim-ledger repo validation). */
+function normalizeRepoFullName(value: unknown): string | null {
+  if (typeof value !== "string") return null;
+  const [owner, repo, extra] = value.trim().split("/");
+  if (!owner || !repo || extra !== undefined) return null;
+  return `${owner}/${repo}`;
+}
+
+function isSoftClaimStatus(value: unknown): value is SoftClaimStatus {
+  return value === "active" || value === "released" || value === "expired";
+}
+
+/**
+ * Build a public-safe soft-claim coordination request from a local claim-ledger record. Pure and network-free.
+ * Returns null when the claim is missing/invalid or carries an unknown status (only the three claim-ledger
+ * statuses map to a request). Only the fixed set of known fields is copied onto the request, so the payload stays
+ * metadata-only by construction.
+ */
+export function buildSoftClaimRequest(claim: unknown, context: SoftClaimRequestContext = {}): SoftClaimRequest | null {
+  if (!claim || typeof claim !== "object" || Array.isArray(claim)) return null;
+  const record = claim as Record<string, unknown>;
+  const repoFullName = normalizeRepoFullName(record.repoFullName);
+  if (repoFullName === null) return null;
+  const issueNumber = record.issueNumber;
+  if (typeof issueNumber !== "number" || !Number.isInteger(issueNumber) || issueNumber <= 0) return null;
+  if (typeof record.claimedAt !== "string" || record.claimedAt.trim() === "") return null;
+  if (!isSoftClaimStatus(record.status)) return null;
+  const note = typeof record.note === "string" && record.note.trim() !== "" ? record.note : null;
+  const instanceId = typeof context.instanceId === "string" && context.instanceId.trim() !== "" ? context.instanceId : null;
+  return {
+    contractVersion: DISCOVERY_INDEX_CONTRACT_VERSION,
+    action: softClaimActionForStatus(record.status),
+    repoFullName,
+    issueNumber,
+    claimedAt: record.claimedAt,
+    note,
+    instanceId,
+  };
+}
diff --git a/packages/gittensory-engine/src/index.ts b/packages/gittensory-engine/src/index.ts
index 2fc4f34606..21240d08c9 100644
--- a/packages/gittensory-engine/src/index.ts
+++ b/packages/gittensory-engine/src/index.ts
@@ -262,6 +262,15 @@ export {
   type ParsedDiscoveryIndexRequest,
   type ParsedDiscoveryIndexResponse,
 } from "./discovery-index-contract.js";
+export {
+  buildSoftClaimRequest,
+  softClaimActionForStatus,
+  type SoftClaimAction,
+  type SoftClaimRecord,
+  type SoftClaimRequest,
+  type SoftClaimRequestContext,
+  type SoftClaimStatus,
+} from "./discovery-soft-claim.js";
 export {
   computeMetadataLaneFit,
   computeMinerGoalLaneFit,
diff --git a/test/unit/discovery-soft-claim.test.ts b/test/unit/discovery-soft-claim.test.ts
new file mode 100644
index 0000000000..4e997fc18c
--- /dev/null
+++ b/test/unit/discovery-soft-claim.test.ts
@@ -0,0 +1,84 @@
+import { describe, expect, it } from "vitest";
+import {
+  DISCOVERY_INDEX_CONTRACT_VERSION,
+  buildSoftClaimRequest,
+  softClaimActionForStatus,
+} from "../../packages/gittensory-engine/src/index";
+
+const ACTIVE_CLAIM = {
+  id: 7,
+  repoFullName: "owner/repo",
+  issueNumber: 42,
+  claimedAt: "2026-01-01T00:00:00Z",
+  status: "active" as const,
+  note: "picked from the miner lane",
+};
+
+describe("soft-claim coordination request builder (#4302)", () => {
+  it("re-exports the builder API from the engine barrel", () => {
+    expect(typeof buildSoftClaimRequest).toBe("function");
+    expect(typeof softClaimActionForStatus).toBe("function");
+  });
+
+  it("builds a public-safe claim request from an active claim, copying only known fields", () => {
+    const req = buildSoftClaimRequest(ACTIVE_CLAIM, { instanceId: "inst-abc" });
+    expect(req).toEqual({
+      contractVersion: DISCOVERY_INDEX_CONTRACT_VERSION,
+      action: "claim",
+      repoFullName: "owner/repo",
+      issueNumber: 42,
+      claimedAt: "2026-01-01T00:00:00Z",
+      note: "picked from the miner lane",
+      instanceId: "inst-abc",
+    });
+    // the local ledger `id` is not leaked into the outbound request
+    expect(Object.keys(req ?? {})).not.toContain("id");
+  });
+
+  it("maps released/expired claims to a release action", () => {
+    expect(softClaimActionForStatus("active")).toBe("claim");
+    expect(softClaimActionForStatus("released")).toBe("release");
+    expect(softClaimActionForStatus("expired")).toBe("release");
+    expect(buildSoftClaimRequest({ ...ACTIVE_CLAIM, status: "released" })?.action).toBe("release");
+    expect(buildSoftClaimRequest({ ...ACTIVE_CLAIM, status: "expired" })?.action).toBe("release");
+  });
+
+  it("normalizes note and instanceId to null when blank, non-string, or absent", () => {
+    expect(buildSoftClaimRequest({ ...ACTIVE_CLAIM, note: "   " })?.note).toBeNull();
+    expect(buildSoftClaimRequest({ ...ACTIVE_CLAIM, note: 5 })?.note).toBeNull();
+    expect(buildSoftClaimRequest({ ...ACTIVE_CLAIM, note: undefined })?.note).toBeNull();
+    expect(buildSoftClaimRequest(ACTIVE_CLAIM)?.instanceId).toBeNull();
+    expect(buildSoftClaimRequest(ACTIVE_CLAIM, { instanceId: "   " })?.instanceId).toBeNull();
+    expect(buildSoftClaimRequest(ACTIVE_CLAIM, { instanceId: 9 as unknown as string })?.instanceId).toBeNull();
+  });
+
+  it("returns null for a non-object claim", () => {
+    for (const bad of [null, undefined, 42, "claim", [ACTIVE_CLAIM]]) {
+      expect(buildSoftClaimRequest(bad)).toBeNull();
+    }
+  });
+
+  it("returns null for an invalid repoFullName", () => {
+    for (const repoFullName of [123, "no-slash", "owner/", "/repo", "a/b/c"]) {
+      expect(buildSoftClaimRequest({ ...ACTIVE_CLAIM, repoFullName })).toBeNull();
+    }
+  });
+
+  it("returns null for an invalid issueNumber", () => {
+    for (const issueNumber of [0, -1, 1.5, "42", undefined]) {
+      expect(buildSoftClaimRequest({ ...ACTIVE_CLAIM, issueNumber })).toBeNull();
+    }
+  });
+
+  it("returns null for a missing/blank/non-string claimedAt", () => {
+    for (const claimedAt of [undefined, "", "   ", 123]) {
+      expect(buildSoftClaimRequest({ ...ACTIVE_CLAIM, claimedAt })).toBeNull();
+    }
+  });
+
+  it("returns null for an unknown claim status", () => {
+    for (const status of ["done", "", undefined, "ACTIVE"]) {
+      expect(buildSoftClaimRequest({ ...ACTIVE_CLAIM, status })).toBeNull();
+    }
+  });
+});