diff --git a/src/miner/soft-claim.ts b/src/miner/soft-claim.ts
new file mode 100644
index 0000000000..67320d846f
--- /dev/null
+++ b/src/miner/soft-claim.ts
@@ -0,0 +1,42 @@
+// #2315 miner soft-claim spec builder. A miner can OPTIONALLY make its claim visible to a fleet by posting a public
+// "soft claim" comment ("a miner is working on this") to reduce duplicate work. This module composes a
+// deterministic, well-formatted claim comment BODY and hands it to the EXISTING `buildPostEligibilityCommentSpec`
+// — it BUILDS the spec only and never executes anything, so the same spec-builder-not-actuator boundary documented
+// by `src/mcp/local-write-tools.ts` (see `LOCAL_WRITE_BOUNDARY`, local-write-tools.ts:8) holds: the miner's OWN
+// harness runs the command with its OWN GitHub credentials. Shell-safety is inherited from the reused builder's
+// single-quote escaping — never re-implemented here.
+import {
+  buildPostEligibilityCommentSpec,
+  type LocalWriteActionSpec,
+} from "../mcp/local-write-tools";
+
+/** Format the deterministic Markdown body of a soft-claim comment: which miner claimed the issue, when, and — when
+ *  provided — when the claim lapses. Pure: the same inputs always produce the same string. The body's shell-safety
+ *  is guaranteed downstream by {@link buildSoftClaimSpec} reusing `local-write-tools`' single-quote escaping. */
+export function buildSoftClaimCommentBody(input: { minerId: string; claimedAt: string; expiresAt?: string }): string {
+  const lines = [
+    `🤖 **Soft claim** — a Gittensor miner (\`${input.minerId}\`) is working on this issue, claimed at ${input.claimedAt}.`,
+  ];
+  if (input.expiresAt) {
+    lines.push(
+      `This claim expires at ${input.expiresAt}; if no PR has landed by then, the issue is open for others again.`,
+    );
+  }
+  lines.push("_Soft claim only — not an assignment. It signals intent so the fleet avoids duplicate work._");
+  return lines.join("\n\n");
+}
+
+/** Build the local-write action spec that posts a soft-claim comment on an issue. Composes
+ *  {@link buildSoftClaimCommentBody} and delegates to the EXISTING `buildPostEligibilityCommentSpec` — reusing its
+ *  shell-safe command construction/escaping rather than duplicating it — so the output stays deterministic and
+ *  single-quote-shell-safe. Builds the spec only; the miner's own harness runs it (see `LOCAL_WRITE_BOUNDARY`). */
+export function buildSoftClaimSpec(input: {
+  repoFullName: string;
+  number: number;
+  minerId: string;
+  claimedAt: string;
+  expiresAt?: string;
+}): LocalWriteActionSpec {
+  const body = buildSoftClaimCommentBody(input);
+  return buildPostEligibilityCommentSpec({ repoFullName: input.repoFullName, number: input.number, body });
+}
diff --git a/test/unit/soft-claim.test.ts b/test/unit/soft-claim.test.ts
new file mode 100644
index 0000000000..81fcf2d113
--- /dev/null
+++ b/test/unit/soft-claim.test.ts
@@ -0,0 +1,52 @@
+import { describe, expect, it } from "vitest";
+import { LOCAL_WRITE_BOUNDARY } from "../../src/mcp/local-write-tools";
+import { buildSoftClaimCommentBody, buildSoftClaimSpec } from "../../src/miner/soft-claim";
+
+describe("soft-claim spec builder (#2315)", () => {
+  it("buildSoftClaimCommentBody: formats a deterministic body with miner id + claimed-at, no expiry line when absent", () => {
+    const body = buildSoftClaimCommentBody({ minerId: "miner-7", claimedAt: "2026-07-03T12:00:00Z" });
+    expect(body).toContain("`miner-7`");
+    expect(body).toContain("claimed at 2026-07-03T12:00:00Z");
+    expect(body).toContain("Soft claim only — not an assignment");
+    expect(body).not.toContain("expires at"); // no expiry note without expiresAt
+    // deterministic
+    expect(buildSoftClaimCommentBody({ minerId: "miner-7", claimedAt: "2026-07-03T12:00:00Z" })).toBe(body);
+  });
+
+  it("buildSoftClaimCommentBody: includes an expiry note when expiresAt is provided", () => {
+    const body = buildSoftClaimCommentBody({
+      minerId: "miner-7",
+      claimedAt: "2026-07-03T12:00:00Z",
+      expiresAt: "2026-07-04T12:00:00Z",
+    });
+    expect(body).toContain("This claim expires at 2026-07-04T12:00:00Z");
+  });
+
+  it("buildSoftClaimSpec: delegates to the eligibility-comment builder, carrying the local-write boundary", () => {
+    const spec = buildSoftClaimSpec({
+      repoFullName: "octo/repo",
+      number: 42,
+      minerId: "miner-7",
+      claimedAt: "2026-07-03T12:00:00Z",
+    });
+    expect(spec.action).toBe("post_eligibility_comment");
+    expect(spec.boundary).toBe(LOCAL_WRITE_BOUNDARY);
+    // the command is the reused builder's shell-safe `gh issue comment`, with the composed body as --body
+    expect(spec.command).toContain("gh issue comment 42 --repo 'octo/repo' --body '");
+    expect(spec.inputs.body).toBe(buildSoftClaimCommentBody({ minerId: "miner-7", claimedAt: "2026-07-03T12:00:00Z" }));
+  });
+
+  it("buildSoftClaimSpec: a single quote in minerId is POSIX-escaped by the reused builder (injection-safe)", () => {
+    const spec = buildSoftClaimSpec({
+      repoFullName: "octo/repo",
+      number: 42,
+      minerId: "evil'; rm -rf / #",
+      claimedAt: "2026-07-03T12:00:00Z",
+    });
+    // the embedded single quote is escaped as '\'' so the command stays a single, safe --body argument
+    expect(spec.command).toContain("evil'\\''; rm -rf / #");
+    // and the whole --body value remains wrapped in one pair of single quotes (no unescaped break-out quote)
+    const unescaped = spec.command.replace(/'\\''/g, "");
+    expect((unescaped.match(/'/g) ?? []).length % 2).toBe(0);
+  });
+});