diff --git a/src/selfhost/config-lint.ts b/src/selfhost/config-lint.ts
new file mode 100644
index 0000000000..7c49f7ba44
--- /dev/null
+++ b/src/selfhost/config-lint.ts
@@ -0,0 +1,126 @@
+import { parse as parseYaml } from "yaml";
+import { MAX_FOCUS_MANIFEST_BYTES, parseFocusManifestContent } from "../signals/focus-manifest";
+
+const TOP_LEVEL_FIELDS = [
+  "source",
+  "wantedPaths",
+  "blockedPaths",
+  "preferredLabels",
+  "linkedIssuePolicy",
+  "testExpectations",
+  "issueDiscoveryPolicy",
+  "maintainerNotes",
+  "publicNotes",
+  "gate",
+  "settings",
+  "review",
+  "features",
+  "contentLane",
+] as const;
+
+const TOP_LEVEL_FIELD_SET = new Set<string>(TOP_LEVEL_FIELDS);
+const NO_RECOGNIZED_FOCUS_FIELDS_WARNING =
+  "Manifest contained no recognized focus fields; falling back to deterministic signals.";
+
+export type SelfHostConfigLintResult = {
+  ok: boolean;
+  warnings: string[];
+  recognizedFields: string[];
+  summary: string;
+};
+
+export function lintManifestText(text: string | null | undefined): SelfHostConfigLintResult {
+  const manifest = parseFocusManifestContent(text, "repo_file");
+  const recognizedFields = recognizedFieldsFor(text);
+  const warnings = [
+    ...manifest.warnings
+      .map(redactManifestWarning)
+      .filter((warning) => recognizedFields.length === 0 || warning !== NO_RECOGNIZED_FOCUS_FIELDS_WARNING),
+    ...unknownTopLevelWarnings(text),
+  ];
+  if (warnings.length === 0 && recognizedFields.length === 0) {
+    warnings.push("Manifest did not define any recognized focus fields.");
+  }
+  const ok = warnings.length === 0 && recognizedFields.length > 0;
+  return {
+    ok,
+    warnings,
+    recognizedFields,
+    summary: ok
+      ? `Manifest parsed ${recognizedFields.length} recognized field${recognizedFields.length === 1 ? "" : "s"}.`
+      : `Manifest has ${warnings.length} warning${warnings.length === 1 ? "" : "s"}.`,
+  };
+}
+
+function recognizedFieldsFor(text: string | null | undefined): string[] {
+  const parsed = parseCanonicalTopLevelObject(text);
+  if (parsed === null) return [];
+  return TOP_LEVEL_FIELDS.filter(
+    (field) => field !== "source" && Object.prototype.hasOwnProperty.call(parsed, field),
+  );
+}
+
+function unknownTopLevelWarnings(text: string | null | undefined): string[] {
+  const raw = text ?? "";
+  const trimmed = raw.trim();
+  if (!trimmed || isOversize(raw)) return [];
+  const parsed = parseTopLevelObject(trimmed);
+  if (parsed === null) return [];
+  const unknown = Object.keys(parsed)
+    .filter((key) => !TOP_LEVEL_FIELD_SET.has(key))
+    .map(formatFieldName);
+  return unknown.length > 0
+    ? [`Manifest contains unknown top-level field${unknown.length === 1 ? "" : "s"}: ${unknown.join(", ")}.`]
+    : [];
+}
+
+function parseCanonicalTopLevelObject(text: string | null | undefined): Record<string, unknown> | null {
+  const raw = text ?? "";
+  const trimmed = raw.trim();
+  if (!trimmed || isOversize(raw)) return null;
+  const looksLikeJson = trimmed.startsWith("{") || trimmed.startsWith("[");
+  try {
+    return topLevelObjectOrNull(looksLikeJson ? JSON.parse(trimmed) : parseYaml(trimmed));
+  } catch {
+    return null;
+  }
+}
+
+function parseTopLevelObject(text: string): Record<string, unknown> | null {
+  const looksLikeJson = text.startsWith("{") || text.startsWith("[");
+  if (looksLikeJson) {
+    try {
+      const parsed = JSON.parse(text);
+      return topLevelObjectOrNull(parsed);
+    } catch {
+      // YAML flow mappings can start with "{" or "[" while still being valid manifest syntax.
+    }
+  }
+  try {
+    return topLevelObjectOrNull(parseYaml(text));
+  } catch {
+    return null;
+  }
+}
+
+function topLevelObjectOrNull(parsed: unknown): Record<string, unknown> | null {
+  return parsed !== null && typeof parsed === "object" && !Array.isArray(parsed)
+    ? (parsed as Record<string, unknown>)
+    : null;
+}
+
+function isOversize(text: string): boolean {
+  return text.length > MAX_FOCUS_MANIFEST_BYTES || new TextEncoder().encode(text).byteLength > MAX_FOCUS_MANIFEST_BYTES;
+}
+
+function formatFieldName(name: string): string {
+  const trimmed = name.replace(/[^\w.-]/g, "_").slice(0, 80);
+  return trimmed || "<blank>";
+}
+
+function redactManifestWarning(warning: string): string {
+  return warning
+    .replace(/; ignoring "[^"]*"\./g, "; ignoring the supplied value.")
+    .replace(/; ignoring "[^"]*"/g, "; ignoring the supplied value")
+    .replace(/falling back to "[^"]*"/g, "falling back to the default");
+}
diff --git a/test/unit/selfhost-config-lint.test.ts b/test/unit/selfhost-config-lint.test.ts
new file mode 100644
index 0000000000..e8f0d3f9a7
--- /dev/null
+++ b/test/unit/selfhost-config-lint.test.ts
@@ -0,0 +1,213 @@
+import { describe, expect, it } from "vitest";
+import { lintManifestText } from "../../src/selfhost/config-lint";
+import { MAX_FOCUS_MANIFEST_BYTES } from "../../src/signals/focus-manifest";
+
+describe("lintManifestText (#2079)", () => {
+  it("passes a valid manifest with one recognized field", () => {
+    expect(lintManifestText("wantedPaths:\n  - src/\n")).toEqual({
+      ok: true,
+      warnings: [],
+      recognizedFields: ["wantedPaths"],
+      summary: "Manifest parsed 1 recognized field.",
+    });
+  });
+
+  it("reports every recognized focus field without echoing values", () => {
+    const result = lintManifestText(`
+wantedPaths: [src/private-policy/]
+blockedPaths: [dist/]
+preferredLabels: [operator-only]
+linkedIssuePolicy: required
+testExpectations: [unit coverage]
+issueDiscoveryPolicy: discouraged
+maintainerNotes: [private maintainer note]
+publicNotes: [keep reviews focused]
+gate:
+  enabled: false
+settings:
+  commentMode: all_prs
+review:
+  profile: chill
+features:
+  rag: true
+contentLane:
+  entryFileGlob: data/*.json
+  collectionField: records
+`);
+
+    expect(result.ok).toBe(true);
+    expect(result.warnings).toEqual([]);
+    expect(result.summary).toBe("Manifest parsed 13 recognized fields.");
+    expect(result.recognizedFields).toEqual([
+      "wantedPaths",
+      "blockedPaths",
+      "preferredLabels",
+      "linkedIssuePolicy",
+      "testExpectations",
+      "issueDiscoveryPolicy",
+      "maintainerNotes",
+      "publicNotes",
+      "gate",
+      "settings",
+      "review",
+      "features",
+      "contentLane",
+    ]);
+    expect(JSON.stringify(result)).not.toContain("private maintainer note");
+    expect(JSON.stringify(result)).not.toContain("operator-only");
+  });
+
+  it("flags empty or fieldless manifests as not ok", () => {
+    expect(lintManifestText(undefined)).toEqual({
+      ok: false,
+      warnings: ["Manifest did not define any recognized focus fields."],
+      recognizedFields: [],
+      summary: "Manifest has 1 warning.",
+    });
+
+    const fieldless = lintManifestText("{}");
+    expect(fieldless.ok).toBe(false);
+    expect(fieldless.recognizedFields).toEqual([]);
+    expect(fieldless.warnings).toEqual(["Manifest contained no recognized focus fields; falling back to deterministic signals."]);
+
+    const scalar = lintManifestText("null");
+    expect(scalar.ok).toBe(false);
+    expect(scalar.recognizedFields).toEqual([]);
+    expect(scalar.warnings).toEqual([
+      "Manifest must be a mapping of fields; ignoring malformed manifest and falling back to deterministic signals.",
+    ]);
+  });
+
+  it("reports explicit default-valued policy fields as recognized", () => {
+    expect(lintManifestText("linkedIssuePolicy: optional\n")).toEqual({
+      ok: true,
+      warnings: [],
+      recognizedFields: ["linkedIssuePolicy"],
+      summary: "Manifest parsed 1 recognized field.",
+    });
+
+    expect(lintManifestText("issueDiscoveryPolicy: neutral\n")).toEqual({
+      ok: true,
+      warnings: [],
+      recognizedFields: ["issueDiscoveryPolicy"],
+      summary: "Manifest parsed 1 recognized field.",
+    });
+  });
+
+  it("accepts source metadata without reporting it as a focus field", () => {
+    expect(lintManifestText("source: repo_file\n")).toEqual({
+      ok: false,
+      warnings: ["Manifest contained no recognized focus fields; falling back to deterministic signals."],
+      recognizedFields: [],
+      summary: "Manifest has 1 warning.",
+    });
+  });
+
+  it("surfaces malformed YAML without adding synthetic unknown-key warnings", () => {
+    const result = lintManifestText("wantedPaths: [unterminated");
+
+    expect(result.ok).toBe(false);
+    expect(result.recognizedFields).toEqual([]);
+    expect(result.warnings).toEqual(["Manifest content was not valid YAML; ignoring it and falling back to deterministic signals."]);
+    expect(result.summary).toBe("Manifest has 1 warning.");
+  });
+
+  it("warns on unknown top-level fields by name only", () => {
+    const result = lintManifestText(`
+unknownSecretKey: super-secret-value
+"": blank-field-name
+"private path": /tmp/private
+`);
+
+    expect(result.ok).toBe(false);
+    expect(result.recognizedFields).toEqual([]);
+    expect(result.summary).toBe("Manifest has 2 warnings.");
+    expect(result.warnings).toEqual([
+      "Manifest contained no recognized focus fields; falling back to deterministic signals.",
+      "Manifest contains unknown top-level fields: unknownSecretKey, <blank>, private_path.",
+    ]);
+    expect(JSON.stringify(result)).not.toContain("super-secret-value");
+    expect(JSON.stringify(result)).not.toContain("/tmp/private");
+  });
+
+  it("uses singular wording for one unknown top-level field", () => {
+    const result = lintManifestText("wantedPaths: [src/]\nunknownSecretKey: super-secret-value\n");
+
+    expect(result.ok).toBe(false);
+    expect(result.recognizedFields).toEqual(["wantedPaths"]);
+    expect(result.warnings).toEqual(["Manifest contains unknown top-level field: unknownSecretKey."]);
+    expect(JSON.stringify(result)).not.toContain("super-secret-value");
+  });
+
+  it("checks unknown fields in YAML flow mappings that start like JSON", () => {
+    const result = lintManifestText("{wantedPaths: [src/], unknownSecretKey: secret}");
+
+    expect(result.ok).toBe(false);
+    expect(result.recognizedFields).toEqual([]);
+    expect(result.warnings).toEqual([
+      "Manifest content was not valid JSON; ignoring it and falling back to deterministic signals.",
+      "Manifest contains unknown top-level field: unknownSecretKey.",
+    ]);
+    expect(JSON.stringify(result)).not.toContain("secret");
+  });
+
+  it("keeps known JSON manifests quiet and non-object JSON invalid", () => {
+    expect(lintManifestText(JSON.stringify({ gate: { enabled: true } }))).toMatchObject({
+      ok: true,
+      warnings: [],
+      recognizedFields: ["gate"],
+    });
+
+    const array = lintManifestText("[]");
+    expect(array.ok).toBe(false);
+    expect(array.warnings).toEqual(["Manifest must be a mapping of fields; ignoring malformed manifest and falling back to deterministic signals."]);
+  });
+
+  it("redacts supplied config values from parser warnings", () => {
+    const result = lintManifestText(`
+linkedIssuePolicy: sometimes
+gate:
+  enabled: true
+  aiReview:
+    provider: secret-provider
+review:
+  profile: secret-profile
+`);
+
+    expect(result.ok).toBe(false);
+    expect(result.recognizedFields).toEqual(["linkedIssuePolicy", "gate", "review"]);
+    expect(result.warnings.join("\n")).toContain("falling back to the default");
+    expect(result.warnings.join("\n")).toContain("ignoring the supplied value");
+    expect(JSON.stringify(result)).not.toContain("sometimes");
+    expect(JSON.stringify(result)).not.toContain("secret-provider");
+    expect(JSON.stringify(result)).not.toContain("secret-profile");
+  });
+
+  it("degrades oversize content without reparsing keys", () => {
+    const asciiOversize = lintManifestText("a".repeat(MAX_FOCUS_MANIFEST_BYTES + 1));
+    expect(asciiOversize.ok).toBe(false);
+    expect(asciiOversize.warnings).toEqual([
+      `Manifest content exceeded ${MAX_FOCUS_MANIFEST_BYTES} bytes; ignoring it and falling back to deterministic signals.`,
+    ]);
+
+    const utf8Oversize = lintManifestText("é".repeat(Math.floor(MAX_FOCUS_MANIFEST_BYTES / 2) + 1));
+    expect(utf8Oversize.ok).toBe(false);
+    expect(utf8Oversize.warnings).toEqual([
+      `Manifest content exceeded ${MAX_FOCUS_MANIFEST_BYTES} bytes; ignoring it and falling back to deterministic signals.`,
+    ]);
+  });
+
+  it("does not reparse padded oversize content after trimming (regression)", () => {
+    const result = lintManifestText(
+      `${" ".repeat(MAX_FOCUS_MANIFEST_BYTES + 1)}unknownSecretKey: super-secret-value\n`,
+    );
+
+    expect(result.ok).toBe(false);
+    expect(result.recognizedFields).toEqual([]);
+    expect(result.warnings).toEqual([
+      `Manifest content exceeded ${MAX_FOCUS_MANIFEST_BYTES} bytes; ignoring it and falling back to deterministic signals.`,
+    ]);
+    expect(JSON.stringify(result)).not.toContain("unknownSecretKey");
+    expect(JSON.stringify(result)).not.toContain("super-secret-value");
+  });
+});