diff --git a/doc/plans/2026-04-24-external-object-reference-backfill.md b/doc/plans/2026-04-24-external-object-reference-backfill.md
new file mode 100644
index 00000000000..02b8e86730c
--- /dev/null
+++ b/doc/plans/2026-04-24-external-object-reference-backfill.md
@@ -0,0 +1,28 @@
+# External Object Reference Backfill
+
+## Purpose
+
+Backfill existing issue titles, descriptions, comments, and documents into `external_object_mentions` after the Phase 3 detector registry and mention sync service exist.
+
+## Command Shape
+
+Add a command parallel to the internal issue-reference backfill:
+
+```sh
+pnpm external-objects:backfill
+pnpm external-objects:backfill -- --company <company-id>
+pnpm external-objects:backfill -- --dry-run
+```
+
+## Required Behavior
+
+- Scan issue title and description sources, issue comments, and issue documents through the same external-object mention sync service used by write hooks.
+- Preserve company boundaries: every scan query, mention upsert, object upsert, and dry-run summary must include `company_id`.
+- Use shared URL extraction and canonicalization helpers so raw URLs, URL userinfo, query strings, and fragments are never persisted.
+- Replace mentions per source instead of appending, using the same source key shape as live write sync.
+- Report counts by company, source kind, provider key, object type, skipped userinfo URLs, and unresolved URLs.
+- Default to a non-interactive safe run; `--dry-run` must avoid writes while still reporting what would change.
+
+## Phase 3 Hook
+
+The command should be implemented only after the detector registry can classify URLs and the service can upsert mentions/placeholders consistently. Until then, Phase 2 owns the schema and shared helpers that make the command safe.
diff --git a/packages/db/src/external-objects-schema.test.ts b/packages/db/src/external-objects-schema.test.ts
new file mode 100644
index 00000000000..897a98d7269
--- /dev/null
+++ b/packages/db/src/external-objects-schema.test.ts
@@ -0,0 +1,47 @@
+import { getTableConfig } from "drizzle-orm/pg-core";
+import { describe, expect, it } from "vitest";
+import { externalObjectMentions } from "./schema/external_object_mentions.js";
+import { externalObjects } from "./schema/external_objects.js";
+
+function indexColumns(table: Parameters<typeof getTableConfig>[0], indexName: string): string[] {
+  const index = getTableConfig(table).indexes.find((candidate) => candidate.config.name === indexName);
+  if (!index) return [];
+  return index.config.columns.map((column) => (column as { name: string }).name);
+}
+
+describe("external object reference schema", () => {
+  it("scopes external object uniqueness by company", () => {
+    expect(indexColumns(externalObjects, "external_objects_company_external_id_uq")).toEqual([
+      "company_id",
+      "provider_key",
+      "object_type",
+      "external_id",
+    ]);
+    expect(indexColumns(externalObjects, "external_objects_company_identity_uq")).toEqual([
+      "company_id",
+      "provider_key",
+      "object_type",
+      "canonical_identity_hash",
+    ]);
+  });
+
+  it("indexes status, refresh scheduling, source issue, and object lookups by company", () => {
+    expect(indexColumns(externalObjects, "external_objects_company_provider_status_idx")).toEqual([
+      "company_id",
+      "provider_key",
+      "status_category",
+    ]);
+    expect(indexColumns(externalObjects, "external_objects_company_refresh_idx")).toEqual([
+      "company_id",
+      "next_refresh_at",
+    ]);
+    expect(indexColumns(externalObjectMentions, "external_object_mentions_company_source_issue_idx")).toEqual([
+      "company_id",
+      "source_issue_id",
+    ]);
+    expect(indexColumns(externalObjectMentions, "external_object_mentions_company_object_idx")).toEqual([
+      "company_id",
+      "object_id",
+    ]);
+  });
+});
diff --git a/packages/db/src/migrations/0106_external_object_references.sql b/packages/db/src/migrations/0106_external_object_references.sql
new file mode 100644
index 00000000000..070a36b4529
--- /dev/null
+++ b/packages/db/src/migrations/0106_external_object_references.sql
@@ -0,0 +1,106 @@
+CREATE TABLE IF NOT EXISTS "external_objects" (
+  "id" uuid PRIMARY KEY DEFAULT gen_random_uuid() NOT NULL,
+  "company_id" uuid NOT NULL,
+  "provider_key" text NOT NULL,
+  "plugin_id" uuid,
+  "object_type" text NOT NULL,
+  "external_id" text NOT NULL,
+  "sanitized_canonical_url" text,
+  "canonical_identity_hash" text,
+  "display_title" text,
+  "status_key" text,
+  "status_label" text,
+  "status_category" text DEFAULT 'unknown' NOT NULL,
+  "status_tone" text DEFAULT 'neutral' NOT NULL,
+  "liveness" text DEFAULT 'unknown' NOT NULL,
+  "is_terminal" boolean DEFAULT false NOT NULL,
+  "data" jsonb DEFAULT '{}'::jsonb NOT NULL,
+  "remote_version" text,
+  "etag" text,
+  "last_resolved_at" timestamp with time zone,
+  "last_changed_at" timestamp with time zone,
+  "last_error_at" timestamp with time zone,
+  "next_refresh_at" timestamp with time zone,
+  "last_error_code" text,
+  "last_error_message" text,
+  "created_at" timestamp with time zone DEFAULT now() NOT NULL,
+  "updated_at" timestamp with time zone DEFAULT now() NOT NULL
+);
+--> statement-breakpoint
+CREATE TABLE IF NOT EXISTS "external_object_mentions" (
+  "id" uuid PRIMARY KEY DEFAULT gen_random_uuid() NOT NULL,
+  "company_id" uuid NOT NULL,
+  "source_issue_id" uuid NOT NULL,
+  "source_kind" text NOT NULL,
+  "source_record_id" uuid,
+  "document_key" text,
+  "property_key" text,
+  "matched_text_redacted" text,
+  "sanitized_display_url" text,
+  "canonical_identity_hash" text,
+  "canonical_identity" jsonb,
+  "object_id" uuid,
+  "provider_key" text,
+  "detector_key" text,
+  "object_type" text,
+  "confidence" text DEFAULT 'exact' NOT NULL,
+  "created_by_plugin_id" uuid,
+  "created_at" timestamp with time zone DEFAULT now() NOT NULL,
+  "updated_at" timestamp with time zone DEFAULT now() NOT NULL
+);
+--> statement-breakpoint
+DO $$ BEGIN
+ ALTER TABLE "external_objects" ADD CONSTRAINT "external_objects_company_id_companies_id_fk" FOREIGN KEY ("company_id") REFERENCES "public"."companies"("id") ON DELETE cascade ON UPDATE no action;
+EXCEPTION
+ WHEN duplicate_object THEN null;
+END $$;
+--> statement-breakpoint
+DO $$ BEGIN
+ ALTER TABLE "external_objects" ADD CONSTRAINT "external_objects_plugin_id_plugins_id_fk" FOREIGN KEY ("plugin_id") REFERENCES "public"."plugins"("id") ON DELETE set null ON UPDATE no action;
+EXCEPTION
+ WHEN duplicate_object THEN null;
+END $$;
+--> statement-breakpoint
+DO $$ BEGIN
+ ALTER TABLE "external_object_mentions" ADD CONSTRAINT "external_object_mentions_company_id_companies_id_fk" FOREIGN KEY ("company_id") REFERENCES "public"."companies"("id") ON DELETE cascade ON UPDATE no action;
+EXCEPTION
+ WHEN duplicate_object THEN null;
+END $$;
+--> statement-breakpoint
+DO $$ BEGIN
+ ALTER TABLE "external_object_mentions" ADD CONSTRAINT "external_object_mentions_source_issue_id_issues_id_fk" FOREIGN KEY ("source_issue_id") REFERENCES "public"."issues"("id") ON DELETE cascade ON UPDATE no action;
+EXCEPTION
+ WHEN duplicate_object THEN null;
+END $$;
+--> statement-breakpoint
+DO $$ BEGIN
+ ALTER TABLE "external_object_mentions" ADD CONSTRAINT "external_object_mentions_object_id_external_objects_id_fk" FOREIGN KEY ("object_id") REFERENCES "public"."external_objects"("id") ON DELETE set null ON UPDATE no action;
+EXCEPTION
+ WHEN duplicate_object THEN null;
+END $$;
+--> statement-breakpoint
+DO $$ BEGIN
+ ALTER TABLE "external_object_mentions" ADD CONSTRAINT "external_object_mentions_created_by_plugin_id_plugins_id_fk" FOREIGN KEY ("created_by_plugin_id") REFERENCES "public"."plugins"("id") ON DELETE set null ON UPDATE no action;
+EXCEPTION
+ WHEN duplicate_object THEN null;
+END $$;
+--> statement-breakpoint
+CREATE INDEX IF NOT EXISTS "external_objects_company_provider_object_idx" ON "external_objects" USING btree ("company_id","provider_key","object_type");
+--> statement-breakpoint
+CREATE INDEX IF NOT EXISTS "external_objects_company_provider_status_idx" ON "external_objects" USING btree ("company_id","provider_key","status_category");
+--> statement-breakpoint
+CREATE INDEX IF NOT EXISTS "external_objects_company_refresh_idx" ON "external_objects" USING btree ("company_id","next_refresh_at");
+--> statement-breakpoint
+CREATE UNIQUE INDEX IF NOT EXISTS "external_objects_company_external_id_uq" ON "external_objects" USING btree ("company_id","provider_key","object_type","external_id");
+--> statement-breakpoint
+CREATE UNIQUE INDEX IF NOT EXISTS "external_objects_company_identity_uq" ON "external_objects" USING btree ("company_id","provider_key","object_type","canonical_identity_hash");
+--> statement-breakpoint
+CREATE INDEX IF NOT EXISTS "external_object_mentions_company_source_issue_idx" ON "external_object_mentions" USING btree ("company_id","source_issue_id");
+--> statement-breakpoint
+CREATE INDEX IF NOT EXISTS "external_object_mentions_company_object_idx" ON "external_object_mentions" USING btree ("company_id","object_id");
+--> statement-breakpoint
+CREATE INDEX IF NOT EXISTS "external_object_mentions_company_provider_idx" ON "external_object_mentions" USING btree ("company_id","provider_key","object_type");
+--> statement-breakpoint
+CREATE UNIQUE INDEX IF NOT EXISTS "external_object_mentions_company_source_record_uq" ON "external_object_mentions" USING btree ("company_id","source_issue_id","source_kind","source_record_id","document_key","property_key","canonical_identity_hash") WHERE "source_record_id" is not null and "canonical_identity_hash" is not null;
+--> statement-breakpoint
+CREATE UNIQUE INDEX IF NOT EXISTS "external_object_mentions_company_source_null_record_uq" ON "external_object_mentions" USING btree ("company_id","source_issue_id","source_kind","document_key","property_key","canonical_identity_hash") WHERE "source_record_id" is null and "canonical_identity_hash" is not null;
diff --git a/packages/db/src/migrations/meta/_journal.json b/packages/db/src/migrations/meta/_journal.json
index ae94c3645b3..4e818013a0c 100644
--- a/packages/db/src/migrations/meta/_journal.json
+++ b/packages/db/src/migrations/meta/_journal.json
@@ -743,6 +743,13 @@
       "when": 1781902000000,
       "tag": "0105_instance_scoped_environments",
       "breakpoints": true
+    },
+    {
+      "idx": 106,
+      "version": "7",
+      "when": 1781902100000,
+      "tag": "0106_external_object_references",
+      "breakpoints": true
     }
   ]
 }
diff --git a/packages/db/src/schema/external_object_mentions.ts b/packages/db/src/schema/external_object_mentions.ts
new file mode 100644
index 00000000000..95cb8e9c80a
--- /dev/null
+++ b/packages/db/src/schema/external_object_mentions.ts
@@ -0,0 +1,61 @@
+import { sql } from "drizzle-orm";
+import { index, jsonb, pgTable, text, timestamp, uniqueIndex, uuid } from "drizzle-orm/pg-core";
+import type { ExternalObjectMentionConfidence, ExternalObjectMentionSourceKind } from "@paperclipai/shared";
+import { companies } from "./companies.js";
+import { externalObjects } from "./external_objects.js";
+import { issues } from "./issues.js";
+import { plugins } from "./plugins.js";
+
+export const externalObjectMentions = pgTable(
+  "external_object_mentions",
+  {
+    id: uuid("id").primaryKey().defaultRandom(),
+    companyId: uuid("company_id").notNull().references(() => companies.id, { onDelete: "cascade" }),
+    sourceIssueId: uuid("source_issue_id").notNull().references(() => issues.id, { onDelete: "cascade" }),
+    sourceKind: text("source_kind").$type<ExternalObjectMentionSourceKind>().notNull(),
+    sourceRecordId: uuid("source_record_id"),
+    documentKey: text("document_key"),
+    propertyKey: text("property_key"),
+    matchedTextRedacted: text("matched_text_redacted"),
+    sanitizedDisplayUrl: text("sanitized_display_url"),
+    canonicalIdentityHash: text("canonical_identity_hash"),
+    canonicalIdentity: jsonb("canonical_identity").$type<Record<string, unknown>>(),
+    objectId: uuid("object_id").references(() => externalObjects.id, { onDelete: "set null" }),
+    providerKey: text("provider_key"),
+    detectorKey: text("detector_key"),
+    objectType: text("object_type"),
+    confidence: text("confidence").$type<ExternalObjectMentionConfidence>().notNull().default("exact"),
+    createdByPluginId: uuid("created_by_plugin_id").references(() => plugins.id, { onDelete: "set null" }),
+    createdAt: timestamp("created_at", { withTimezone: true }).notNull().defaultNow(),
+    updatedAt: timestamp("updated_at", { withTimezone: true }).notNull().defaultNow(),
+  },
+  (table) => ({
+    companySourceIssueIdx: index("external_object_mentions_company_source_issue_idx").on(
+      table.companyId,
+      table.sourceIssueId,
+    ),
+    companyObjectIdx: index("external_object_mentions_company_object_idx").on(table.companyId, table.objectId),
+    companyProviderIdx: index("external_object_mentions_company_provider_idx").on(
+      table.companyId,
+      table.providerKey,
+      table.objectType,
+    ),
+    companySourceMentionWithRecordUq: uniqueIndex("external_object_mentions_company_source_record_uq").on(
+      table.companyId,
+      table.sourceIssueId,
+      table.sourceKind,
+      table.sourceRecordId,
+      table.documentKey,
+      table.propertyKey,
+      table.canonicalIdentityHash,
+    ).where(sql`${table.sourceRecordId} is not null and ${table.canonicalIdentityHash} is not null`),
+    companySourceMentionWithoutRecordUq: uniqueIndex("external_object_mentions_company_source_null_record_uq").on(
+      table.companyId,
+      table.sourceIssueId,
+      table.sourceKind,
+      table.documentKey,
+      table.propertyKey,
+      table.canonicalIdentityHash,
+    ).where(sql`${table.sourceRecordId} is null and ${table.canonicalIdentityHash} is not null`),
+  }),
+);
diff --git a/packages/db/src/schema/external_objects.ts b/packages/db/src/schema/external_objects.ts
new file mode 100644
index 00000000000..d3028adef9e
--- /dev/null
+++ b/packages/db/src/schema/external_objects.ts
@@ -0,0 +1,74 @@
+import {
+  boolean,
+  index,
+  jsonb,
+  pgTable,
+  text,
+  timestamp,
+  uniqueIndex,
+  uuid,
+} from "drizzle-orm/pg-core";
+import type {
+  ExternalObjectLivenessState,
+  ExternalObjectStatusCategory,
+  ExternalObjectStatusTone,
+} from "@paperclipai/shared";
+import { companies } from "./companies.js";
+import { plugins } from "./plugins.js";
+
+export const externalObjects = pgTable(
+  "external_objects",
+  {
+    id: uuid("id").primaryKey().defaultRandom(),
+    companyId: uuid("company_id").notNull().references(() => companies.id, { onDelete: "cascade" }),
+    providerKey: text("provider_key").notNull(),
+    pluginId: uuid("plugin_id").references(() => plugins.id, { onDelete: "set null" }),
+    objectType: text("object_type").notNull(),
+    externalId: text("external_id").notNull(),
+    sanitizedCanonicalUrl: text("sanitized_canonical_url"),
+    canonicalIdentityHash: text("canonical_identity_hash"),
+    displayTitle: text("display_title"),
+    statusKey: text("status_key"),
+    statusLabel: text("status_label"),
+    statusCategory: text("status_category").$type<ExternalObjectStatusCategory>().notNull().default("unknown"),
+    statusTone: text("status_tone").$type<ExternalObjectStatusTone>().notNull().default("neutral"),
+    liveness: text("liveness").$type<ExternalObjectLivenessState>().notNull().default("unknown"),
+    isTerminal: boolean("is_terminal").notNull().default(false),
+    data: jsonb("data").$type<Record<string, unknown>>().notNull().default({}),
+    remoteVersion: text("remote_version"),
+    etag: text("etag"),
+    lastResolvedAt: timestamp("last_resolved_at", { withTimezone: true }),
+    lastChangedAt: timestamp("last_changed_at", { withTimezone: true }),
+    lastErrorAt: timestamp("last_error_at", { withTimezone: true }),
+    nextRefreshAt: timestamp("next_refresh_at", { withTimezone: true }),
+    lastErrorCode: text("last_error_code"),
+    lastErrorMessage: text("last_error_message"),
+    createdAt: timestamp("created_at", { withTimezone: true }).notNull().defaultNow(),
+    updatedAt: timestamp("updated_at", { withTimezone: true }).notNull().defaultNow(),
+  },
+  (table) => ({
+    companyProviderObjectIdx: index("external_objects_company_provider_object_idx").on(
+      table.companyId,
+      table.providerKey,
+      table.objectType,
+    ),
+    companyProviderStatusIdx: index("external_objects_company_provider_status_idx").on(
+      table.companyId,
+      table.providerKey,
+      table.statusCategory,
+    ),
+    companyRefreshIdx: index("external_objects_company_refresh_idx").on(table.companyId, table.nextRefreshAt),
+    companyExternalIdUq: uniqueIndex("external_objects_company_external_id_uq").on(
+      table.companyId,
+      table.providerKey,
+      table.objectType,
+      table.externalId,
+    ),
+    companyCanonicalIdentityUq: uniqueIndex("external_objects_company_identity_uq").on(
+      table.companyId,
+      table.providerKey,
+      table.objectType,
+      table.canonicalIdentityHash,
+    ),
+  }),
+);
diff --git a/packages/db/src/schema/index.ts b/packages/db/src/schema/index.ts
index cda88aedbef..5b2d9e1a496 100644
--- a/packages/db/src/schema/index.ts
+++ b/packages/db/src/schema/index.ts
@@ -36,6 +36,8 @@ export { issueWatchdogs } from "./issue_watchdogs.js";
 export { issuePlanDecompositions } from "./issue_plan_decompositions.js";
 export { issueRecoveryActions } from "./issue_recovery_actions.js";
 export { issueReferenceMentions } from "./issue_reference_mentions.js";
+export { externalObjects } from "./external_objects.js";
+export { externalObjectMentions } from "./external_object_mentions.js";
 export { issueRelations } from "./issue_relations.js";
 export { routines, routineRevisions, routineTriggers, routineRuns } from "./routines.js";
 export { issueWorkProducts } from "./issue_work_products.js";
diff --git a/packages/shared/src/constants.ts b/packages/shared/src/constants.ts
index 5ec46818888..e1db31cc979 100644
--- a/packages/shared/src/constants.ts
+++ b/packages/shared/src/constants.ts
@@ -358,6 +358,53 @@ export const DOCUMENT_ANNOTATION_ANCHOR_CONFIDENCES = [
 export type DocumentAnnotationAnchorConfidence =
   (typeof DOCUMENT_ANNOTATION_ANCHOR_CONFIDENCES)[number];
 
+export const EXTERNAL_OBJECT_STATUS_CATEGORIES = [
+  "unknown",
+  "open",
+  "waiting",
+  "running",
+  "succeeded",
+  "failed",
+  "blocked",
+  "closed",
+  "archived",
+  "auth_required",
+  "unreachable",
+] as const;
+export type ExternalObjectStatusCategory = (typeof EXTERNAL_OBJECT_STATUS_CATEGORIES)[number];
+
+export const EXTERNAL_OBJECT_STATUS_TONES = [
+  "neutral",
+  "info",
+  "success",
+  "warning",
+  "danger",
+  "muted",
+] as const;
+export type ExternalObjectStatusTone = (typeof EXTERNAL_OBJECT_STATUS_TONES)[number];
+
+export const EXTERNAL_OBJECT_LIVENESS_STATES = [
+  "unknown",
+  "fresh",
+  "stale",
+  "auth_required",
+  "unreachable",
+] as const;
+export type ExternalObjectLivenessState = (typeof EXTERNAL_OBJECT_LIVENESS_STATES)[number];
+
+export const EXTERNAL_OBJECT_MENTION_SOURCE_KINDS = [
+  "title",
+  "description",
+  "comment",
+  "document",
+  "property",
+  "plugin",
+] as const;
+export type ExternalObjectMentionSourceKind = (typeof EXTERNAL_OBJECT_MENTION_SOURCE_KINDS)[number];
+
+export const EXTERNAL_OBJECT_MENTION_CONFIDENCES = ["exact", "likely", "possible"] as const;
+export type ExternalObjectMentionConfidence = (typeof EXTERNAL_OBJECT_MENTION_CONFIDENCES)[number];
+
 export const ISSUE_EXECUTION_POLICY_MODES = ["normal", "auto"] as const;
 export type IssueExecutionPolicyMode = (typeof ISSUE_EXECUTION_POLICY_MODES)[number];
 
diff --git a/packages/shared/src/external-objects.test.ts b/packages/shared/src/external-objects.test.ts
new file mode 100644
index 00000000000..0c0d5457087
--- /dev/null
+++ b/packages/shared/src/external-objects.test.ts
@@ -0,0 +1,126 @@
+import { describe, expect, it } from "vitest";
+import {
+  buildExternalObjectMentionSourceKey,
+  buildExternalObjectScopedIdentityKey,
+  canonicalizeExternalObjectUrl,
+  extractExternalObjectCanonicalUrls,
+  findExternalObjectUrlMatches,
+  formatExternalObjectMentionSourceLabel,
+} from "./external-objects.js";
+import { externalObjectProviderKeySchema, externalObjectTypeSchema } from "./validators/external-object.js";
+
+describe("external object references", () => {
+  it("extracts external urls without changing internal issue reference behavior", () => {
+    expect(
+      findExternalObjectUrlMatches(
+        "See PAP-1, /issues/PAP-2, https://paperclip.ing/PAP/issues/PAP-3, and https://github.com/acme/app/pull/4.",
+      ),
+    ).toEqual([{ index: 70, length: 34, matchedText: "https://github.com/acme/app/pull/4" }]);
+  });
+
+  it("ignores urls inside inline and fenced code", () => {
+    const markdown = [
+      "Use https://github.com/acme/app/pull/1 here.",
+      "`https://github.com/acme/app/pull/2` should not count.",
+      "```",
+      "https://github.com/acme/app/pull/3",
+      "```",
+    ].join("\n");
+
+    expect(findExternalObjectUrlMatches(markdown).map((match) => match.matchedText)).toEqual([
+      "https://github.com/acme/app/pull/1",
+    ]);
+  });
+
+  it("canonicalizes urls by stripping query and fragment by default", () => {
+    expect(canonicalizeExternalObjectUrl("HTTPS://GitHub.com/acme/app/pull/1?token=secret#discussion")).toMatchObject({
+      sanitizedCanonicalUrl: "https://github.com/acme/app/pull/1",
+      sanitizedDisplayUrl: "https://github.com/acme/app/pull/1",
+      redactedMatchedText: "https://github.com/acme/app/pull/1",
+      canonicalIdentity: {
+        scheme: "https",
+        host: "github.com",
+        path: "/acme/app/pull/1",
+      },
+    });
+  });
+
+  it("rejects urls with userinfo", () => {
+    expect(canonicalizeExternalObjectUrl("https://token:secret@github.com/acme/app/pull/1")).toBeNull();
+  });
+
+  it("hashes provider-required query identity values without storing plaintext", () => {
+    const first = canonicalizeExternalObjectUrl("https://deploy.test/run?id=secret-run&token=drop", {
+      identityQueryParams: ["id"],
+    });
+    const second = canonicalizeExternalObjectUrl("https://deploy.test/run?id=secret-run&token=other", {
+      identityQueryParams: ["id"],
+    });
+
+    expect(first?.sanitizedCanonicalUrl).toBe("https://deploy.test/run");
+    expect(first?.canonicalIdentity.queryParamHashes?.id).toHaveLength(64);
+    expect(first?.canonicalIdentity.queryParamHashes?.id).not.toContain("secret-run");
+    expect(second?.canonicalIdentityHash).toBe(first?.canonicalIdentityHash);
+  });
+
+  it("dedupes extracted canonical urls by canonical identity", () => {
+    expect(
+      extractExternalObjectCanonicalUrls(
+        "https://github.com/acme/app/pull/1?token=a and https://github.com/acme/app/pull/1#discussion",
+      ).map((entry) => entry.sanitizedCanonicalUrl),
+    ).toEqual(["https://github.com/acme/app/pull/1"]);
+  });
+
+  it("includes company id in scoped object identity keys", () => {
+    const base = {
+      providerKey: "github",
+      objectType: "pull_request",
+      canonicalIdentityHash: "hash",
+    };
+
+    expect(buildExternalObjectScopedIdentityKey({ companyId: "company-a", ...base })).not.toBe(
+      buildExternalObjectScopedIdentityKey({ companyId: "company-b", ...base }),
+    );
+  });
+
+  it("builds source keys for replacing mentions from the same source", () => {
+    const oldMentionSource = buildExternalObjectMentionSourceKey({
+      companyId: "company-a",
+      sourceIssueId: "issue-1",
+      sourceKind: "comment",
+      sourceRecordId: "comment-1",
+    });
+    const newMentionSource = buildExternalObjectMentionSourceKey({
+      companyId: "company-a",
+      sourceIssueId: "issue-1",
+      sourceKind: "comment",
+      sourceRecordId: "comment-1",
+    });
+    const anotherCompanySource = buildExternalObjectMentionSourceKey({
+      companyId: "company-b",
+      sourceIssueId: "issue-1",
+      sourceKind: "comment",
+      sourceRecordId: "comment-1",
+    });
+
+    expect(newMentionSource).toBe(oldMentionSource);
+    expect(anotherCompanySource).not.toBe(oldMentionSource);
+  });
+
+  it("formats stable source labels", () => {
+    expect(formatExternalObjectMentionSourceLabel({ sourceKind: "title" })).toBe("Title");
+    expect(formatExternalObjectMentionSourceLabel({ sourceKind: "document", documentKey: "plan" })).toBe(
+      "Document: plan",
+    );
+    expect(formatExternalObjectMentionSourceLabel({ sourceKind: "property", propertyKey: "pr" })).toBe(
+      "Property: pr",
+    );
+  });
+
+  it("validates provider keys and object types", () => {
+    expect(externalObjectProviderKeySchema.parse("github.enterprise")).toBe("github.enterprise");
+    expect(externalObjectTypeSchema.parse("pull_request")).toBe("pull_request");
+    expect(externalObjectProviderKeySchema.safeParse("GitHub").success).toBe(false);
+    expect(externalObjectTypeSchema.safeParse("pull-request").success).toBe(false);
+  });
+});
diff --git a/packages/shared/src/external-objects.ts b/packages/shared/src/external-objects.ts
new file mode 100644
index 00000000000..443ab43033d
--- /dev/null
+++ b/packages/shared/src/external-objects.ts
@@ -0,0 +1,262 @@
+import { createHash } from "node:crypto";
+import type { ExternalObjectMentionSourceKind } from "./constants.js";
+import { parseIssueReferenceHref } from "./issue-references.js";
+
+export interface ExternalObjectUrlMatch {
+  index: number;
+  length: number;
+  matchedText: string;
+}
+
+export interface ExternalObjectCanonicalIdentity {
+  scheme: "http" | "https";
+  host: string;
+  path: string;
+  queryParamHashes?: Record<string, string>;
+}
+
+export interface ExternalObjectUrlCanonicalizationOptions {
+  identityQueryParams?: readonly string[];
+}
+
+export interface ExternalObjectCanonicalUrl {
+  sanitizedCanonicalUrl: string;
+  sanitizedDisplayUrl: string;
+  canonicalIdentity: ExternalObjectCanonicalIdentity;
+  canonicalIdentityHash: string;
+  redactedMatchedText: string;
+}
+
+export interface ExternalObjectMentionSource {
+  companyId?: string;
+  sourceIssueId?: string;
+  sourceKind: ExternalObjectMentionSourceKind;
+  sourceRecordId?: string | null;
+  documentKey?: string | null;
+  propertyKey?: string | null;
+}
+
+const EXTERNAL_URL_TOKEN_RE = /https?:\/\/[^\s<>()]+/gi;
+
+function preserveNewlinesAsWhitespace(value: string) {
+  return value.replace(/[^\n]/g, " ");
+}
+
+function stripMarkdownCode(markdown: string): string {
+  if (!markdown) return "";
+
+  let output = "";
+  let index = 0;
+
+  while (index < markdown.length) {
+    const remaining = markdown.slice(index);
+    const fenceMatch = /^(?:```+|~~~+)/.exec(remaining);
+    const atLineStart = index === 0 || markdown[index - 1] === "\n";
+
+    if (atLineStart && fenceMatch) {
+      const fence = fenceMatch[0]!;
+      const blockStart = index;
+      index += fence.length;
+      while (index < markdown.length && markdown[index] !== "\n") index += 1;
+      if (index < markdown.length) index += 1;
+
+      while (index < markdown.length) {
+        const lineStart = index === 0 || markdown[index - 1] === "\n";
+        if (lineStart && markdown.startsWith(fence, index)) {
+          index += fence.length;
+          while (index < markdown.length && markdown[index] !== "\n") index += 1;
+          if (index < markdown.length) index += 1;
+          break;
+        }
+        index += 1;
+      }
+
+      output += preserveNewlinesAsWhitespace(markdown.slice(blockStart, index));
+      continue;
+    }
+
+    if (markdown[index] === "`") {
+      let tickCount = 1;
+      while (index + tickCount < markdown.length && markdown[index + tickCount] === "`") {
+        tickCount += 1;
+      }
+      const fence = "`".repeat(tickCount);
+      const inlineStart = index;
+      index += tickCount;
+      const closeIndex = markdown.indexOf(fence, index);
+      if (closeIndex === -1) {
+        output += markdown.slice(inlineStart, inlineStart + tickCount);
+        index = inlineStart + tickCount;
+        continue;
+      }
+      index = closeIndex + tickCount;
+      output += preserveNewlinesAsWhitespace(markdown.slice(inlineStart, index));
+      continue;
+    }
+
+    output += markdown[index]!;
+    index += 1;
+  }
+
+  return output;
+}
+
+function trimTrailingPunctuation(token: string): string {
+  let trimmed = token;
+  while (trimmed.length > 0) {
+    const last = trimmed[trimmed.length - 1]!;
+    if (!".,!?;:".includes(last) && last !== ")" && last !== "]") break;
+
+    if (
+      (last === ")" && (trimmed.match(/\(/g)?.length ?? 0) >= (trimmed.match(/\)/g)?.length ?? 0))
+      || (last === "]" && (trimmed.match(/\[/g)?.length ?? 0) >= (trimmed.match(/\]/g)?.length ?? 0))
+    ) {
+      break;
+    }
+    trimmed = trimmed.slice(0, -1);
+  }
+  return trimmed;
+}
+
+function sha256Hex(value: string): string {
+  return createHash("sha256").update(value).digest("hex");
+}
+
+function stableStringify(value: unknown): string {
+  if (Array.isArray(value)) {
+    return `[${value.map((entry) => stableStringify(entry)).join(",")}]`;
+  }
+  if (value && typeof value === "object") {
+    const record = value as Record<string, unknown>;
+    return `{${Object.keys(record)
+      .sort()
+      .map((key) => `${JSON.stringify(key)}:${stableStringify(record[key])}`)
+      .join(",")}}`;
+  }
+  return JSON.stringify(value);
+}
+
+function normalizePathname(pathname: string): string {
+  return pathname || "/";
+}
+
+export function findExternalObjectUrlMatches(markdown: string): ExternalObjectUrlMatch[] {
+  if (!markdown) return [];
+
+  const scrubbed = stripMarkdownCode(markdown);
+  const matches: ExternalObjectUrlMatch[] = [];
+  let match: RegExpExecArray | null;
+  const re = new RegExp(EXTERNAL_URL_TOKEN_RE);
+
+  while ((match = re.exec(scrubbed)) !== null) {
+    const matchedText = trimTrailingPunctuation(match[0]);
+    if (!matchedText || parseIssueReferenceHref(matchedText)) continue;
+
+    matches.push({
+      index: match.index,
+      length: matchedText.length,
+      matchedText,
+    });
+  }
+
+  return matches;
+}
+
+export function canonicalizeExternalObjectUrl(
+  value: string,
+  options: ExternalObjectUrlCanonicalizationOptions = {},
+): ExternalObjectCanonicalUrl | null {
+  let url: URL;
+  try {
+    url = new URL(value.trim());
+  } catch {
+    return null;
+  }
+
+  if (url.protocol !== "http:" && url.protocol !== "https:") return null;
+  if (url.username || url.password) return null;
+
+  const scheme = url.protocol === "https:" ? "https" : "http";
+  const path = normalizePathname(url.pathname);
+  const sanitizedCanonicalUrl = `${scheme}://${url.host.toLowerCase()}${path}`;
+  const identityQueryParams = new Set(options.identityQueryParams ?? []);
+  const queryParamHashes: Record<string, string> = {};
+
+  for (const key of [...identityQueryParams].sort()) {
+    const values = url.searchParams.getAll(key);
+    if (values.length === 0) continue;
+    queryParamHashes[key] = sha256Hex(values.join("\u0000"));
+  }
+
+  const canonicalIdentity: ExternalObjectCanonicalIdentity = {
+    scheme,
+    host: url.host.toLowerCase(),
+    path,
+    ...(Object.keys(queryParamHashes).length > 0 ? { queryParamHashes } : {}),
+  };
+
+  return {
+    sanitizedCanonicalUrl,
+    sanitizedDisplayUrl: sanitizedCanonicalUrl,
+    canonicalIdentity,
+    canonicalIdentityHash: sha256Hex(stableStringify(canonicalIdentity)),
+    redactedMatchedText: sanitizedCanonicalUrl,
+  };
+}
+
+export function extractExternalObjectCanonicalUrls(
+  markdown: string,
+  options: ExternalObjectUrlCanonicalizationOptions = {},
+): ExternalObjectCanonicalUrl[] {
+  const seen = new Set<string>();
+  const ordered: ExternalObjectCanonicalUrl[] = [];
+
+  for (const match of findExternalObjectUrlMatches(markdown)) {
+    const canonical = canonicalizeExternalObjectUrl(match.matchedText, options);
+    if (!canonical || seen.has(canonical.canonicalIdentityHash)) continue;
+    seen.add(canonical.canonicalIdentityHash);
+    ordered.push(canonical);
+  }
+
+  return ordered;
+}
+
+export function buildExternalObjectScopedIdentityKey(args: {
+  companyId: string;
+  providerKey: string;
+  objectType: string;
+  canonicalIdentityHash: string;
+}): string {
+  return [args.companyId, args.providerKey, args.objectType, args.canonicalIdentityHash].join(":");
+}
+
+export function buildExternalObjectMentionSourceKey(source: Required<Pick<
+  ExternalObjectMentionSource,
+  "companyId" | "sourceIssueId" | "sourceKind"
+>> & ExternalObjectMentionSource): string {
+  return [
+    source.companyId,
+    source.sourceIssueId,
+    source.sourceKind,
+    source.sourceRecordId ?? "",
+    source.documentKey ?? "",
+    source.propertyKey ?? "",
+  ].join(":");
+}
+
+export function formatExternalObjectMentionSourceLabel(source: ExternalObjectMentionSource): string {
+  switch (source.sourceKind) {
+    case "title":
+      return "Title";
+    case "description":
+      return "Description";
+    case "comment":
+      return "Comment";
+    case "document":
+      return source.documentKey ? `Document: ${source.documentKey}` : "Document";
+    case "property":
+      return source.propertyKey ? `Property: ${source.propertyKey}` : "Property";
+    case "plugin":
+      return "Plugin";
+  }
+}
diff --git a/packages/shared/src/index.ts b/packages/shared/src/index.ts
index 319f484f9f8..2ecec888d1f 100644
--- a/packages/shared/src/index.ts
+++ b/packages/shared/src/index.ts
@@ -92,6 +92,11 @@ export {
   DOCUMENT_ANNOTATION_THREAD_STATUSES,
   DOCUMENT_ANNOTATION_ANCHOR_STATES,
   DOCUMENT_ANNOTATION_ANCHOR_CONFIDENCES,
+  EXTERNAL_OBJECT_STATUS_CATEGORIES,
+  EXTERNAL_OBJECT_STATUS_TONES,
+  EXTERNAL_OBJECT_LIVENESS_STATES,
+  EXTERNAL_OBJECT_MENTION_SOURCE_KINDS,
+  EXTERNAL_OBJECT_MENTION_CONFIDENCES,
   ISSUE_EXECUTION_POLICY_MODES,
   ISSUE_EXECUTION_STAGE_TYPES,
   ISSUE_MONITOR_SCHEDULED_BY,
@@ -217,6 +222,11 @@ export {
   type DocumentAnnotationThreadStatus,
   type DocumentAnnotationAnchorState,
   type DocumentAnnotationAnchorConfidence,
+  type ExternalObjectStatusCategory,
+  type ExternalObjectStatusTone,
+  type ExternalObjectLivenessState,
+  type ExternalObjectMentionSourceKind,
+  type ExternalObjectMentionConfidence,
   type IssueExecutionPolicyMode,
   type IssueExecutionStageType,
   type IssueMonitorScheduledBy,
@@ -522,6 +532,8 @@ export type {
   DocumentTextRange,
   UpdateDocumentAnnotationThreadRequest,
   AttachmentArtifactWorkProductMetadata,
+  ExternalObject,
+  ExternalObjectMention,
   Issue,
   IssueAssigneeAdapterOverrides,
   IssueBlockerAttention,
@@ -829,6 +841,20 @@ export {
   type VerifyDocumentAnchorSelectorResult,
 } from "./document-anchors.js";
 
+export {
+  buildExternalObjectScopedIdentityKey,
+  buildExternalObjectMentionSourceKey,
+  canonicalizeExternalObjectUrl,
+  extractExternalObjectCanonicalUrls,
+  findExternalObjectUrlMatches,
+  formatExternalObjectMentionSourceLabel,
+  type ExternalObjectCanonicalIdentity,
+  type ExternalObjectCanonicalUrl,
+  type ExternalObjectMentionSource,
+  type ExternalObjectUrlCanonicalizationOptions,
+  type ExternalObjectUrlMatch,
+} from "./external-objects.js";
+
 export {
   sidebarOrderPreferenceSchema,
   upsertSidebarOrderPreferenceSchema,
@@ -924,11 +950,24 @@ export {
   feedbackTargetTypeSchema,
   feedbackTraceStatusSchema,
   feedbackVoteValueSchema,
+  externalObjectStatusCategorySchema,
+  externalObjectStatusToneSchema,
+  externalObjectLivenessStateSchema,
+  externalObjectMentionSourceKindSchema,
+  externalObjectMentionConfidenceSchema,
+  externalObjectProviderKeySchema,
+  externalObjectTypeSchema,
+  externalObjectCanonicalIdentitySchema,
+  externalObjectMentionSourceSchema,
   upsertIssueFeedbackVoteSchema,
   type CreateCompany,
   type UpdateCompany,
   type UpdateCompanyBranding,
   type UpsertIssueFeedbackVote,
+  type ExternalObjectCanonicalIdentityInput,
+  type ExternalObjectMentionSourceInput,
+  type ExternalObjectProviderKeyInput,
+  type ExternalObjectTypeInput,
   environmentDriverSchema,
   environmentStatusSchema,
   environmentLeaseStatusSchema,
diff --git a/packages/shared/src/types/external-object.ts b/packages/shared/src/types/external-object.ts
new file mode 100644
index 00000000000..3c785079a7b
--- /dev/null
+++ b/packages/shared/src/types/external-object.ts
@@ -0,0 +1,58 @@
+import type {
+  ExternalObjectLivenessState,
+  ExternalObjectMentionConfidence,
+  ExternalObjectMentionSourceKind,
+  ExternalObjectStatusCategory,
+  ExternalObjectStatusTone,
+} from "../constants.js";
+
+export interface ExternalObject {
+  id: string;
+  companyId: string;
+  providerKey: string;
+  pluginId: string | null;
+  objectType: string;
+  externalId: string;
+  sanitizedCanonicalUrl: string | null;
+  canonicalIdentityHash: string | null;
+  displayTitle: string | null;
+  statusKey: string | null;
+  statusLabel: string | null;
+  statusCategory: ExternalObjectStatusCategory;
+  statusTone: ExternalObjectStatusTone;
+  liveness: ExternalObjectLivenessState;
+  isTerminal: boolean;
+  data: Record<string, unknown>;
+  remoteVersion: string | null;
+  etag: string | null;
+  lastResolvedAt: string | null;
+  lastChangedAt: string | null;
+  lastErrorAt: string | null;
+  nextRefreshAt: string | null;
+  lastErrorCode: string | null;
+  lastErrorMessage: string | null;
+  createdAt: string;
+  updatedAt: string;
+}
+
+export interface ExternalObjectMention {
+  id: string;
+  companyId: string;
+  sourceIssueId: string;
+  sourceKind: ExternalObjectMentionSourceKind;
+  sourceRecordId: string | null;
+  documentKey: string | null;
+  propertyKey: string | null;
+  matchedTextRedacted: string | null;
+  sanitizedDisplayUrl: string | null;
+  canonicalIdentityHash: string | null;
+  canonicalIdentity: Record<string, unknown> | null;
+  objectId: string | null;
+  providerKey: string | null;
+  detectorKey: string | null;
+  objectType: string | null;
+  confidence: ExternalObjectMentionConfidence;
+  createdByPluginId: string | null;
+  createdAt: string;
+  updatedAt: string;
+}
diff --git a/packages/shared/src/types/index.ts b/packages/shared/src/types/index.ts
index 5354d5ea4f8..ac3d2d3e21e 100644
--- a/packages/shared/src/types/index.ts
+++ b/packages/shared/src/types/index.ts
@@ -265,6 +265,11 @@ export type {
   CompanyArtifactSource,
   CompanyArtifactsResponse,
 } from "./artifact.js";
+
+export type {
+  ExternalObject,
+  ExternalObjectMention,
+} from "./external-object.js";
 export type {
   Issue,
   IssueWorkMode,
diff --git a/packages/shared/src/validators/external-object.ts b/packages/shared/src/validators/external-object.ts
new file mode 100644
index 00000000000..33ae0ce4900
--- /dev/null
+++ b/packages/shared/src/validators/external-object.ts
@@ -0,0 +1,38 @@
+import { z } from "zod";
+import {
+  EXTERNAL_OBJECT_LIVENESS_STATES,
+  EXTERNAL_OBJECT_MENTION_CONFIDENCES,
+  EXTERNAL_OBJECT_MENTION_SOURCE_KINDS,
+  EXTERNAL_OBJECT_STATUS_CATEGORIES,
+  EXTERNAL_OBJECT_STATUS_TONES,
+} from "../constants.js";
+
+export const externalObjectStatusCategorySchema = z.enum(EXTERNAL_OBJECT_STATUS_CATEGORIES);
+export const externalObjectStatusToneSchema = z.enum(EXTERNAL_OBJECT_STATUS_TONES);
+export const externalObjectLivenessStateSchema = z.enum(EXTERNAL_OBJECT_LIVENESS_STATES);
+export const externalObjectMentionSourceKindSchema = z.enum(EXTERNAL_OBJECT_MENTION_SOURCE_KINDS);
+export const externalObjectMentionConfidenceSchema = z.enum(EXTERNAL_OBJECT_MENTION_CONFIDENCES);
+export const externalObjectProviderKeySchema = z.string().trim().min(1).max(80).regex(/^[a-z][a-z0-9_.-]*$/);
+export const externalObjectTypeSchema = z.string().trim().min(1).max(80).regex(/^[a-z][a-z0-9_]*$/);
+
+export const externalObjectCanonicalIdentitySchema = z
+  .object({
+    scheme: z.enum(["http", "https"]),
+    host: z.string().trim().min(1),
+    path: z.string().trim().min(1),
+    queryParamHashes: z.record(z.string().regex(/^[a-f0-9]{64}$/)).optional(),
+  })
+  .strict();
+
+export const externalObjectMentionSourceSchema = z
+  .object({
+    sourceKind: externalObjectMentionSourceKindSchema,
+    documentKey: z.string().trim().min(1).optional().nullable(),
+    propertyKey: z.string().trim().min(1).optional().nullable(),
+  })
+  .strict();
+
+export type ExternalObjectCanonicalIdentityInput = z.infer<typeof externalObjectCanonicalIdentitySchema>;
+export type ExternalObjectMentionSourceInput = z.infer<typeof externalObjectMentionSourceSchema>;
+export type ExternalObjectProviderKeyInput = z.infer<typeof externalObjectProviderKeySchema>;
+export type ExternalObjectTypeInput = z.infer<typeof externalObjectTypeSchema>;
diff --git a/packages/shared/src/validators/index.ts b/packages/shared/src/validators/index.ts
index 6323a7dc880..b04e1533d78 100644
--- a/packages/shared/src/validators/index.ts
+++ b/packages/shared/src/validators/index.ts
@@ -59,6 +59,22 @@ export {
   updateResourceMembershipSchema,
   type UpdateResourceMembership,
 } from "./resource-memberships.js";
+
+export {
+  externalObjectStatusCategorySchema,
+  externalObjectStatusToneSchema,
+  externalObjectLivenessStateSchema,
+  externalObjectMentionSourceKindSchema,
+  externalObjectMentionConfidenceSchema,
+  externalObjectProviderKeySchema,
+  externalObjectTypeSchema,
+  externalObjectCanonicalIdentitySchema,
+  externalObjectMentionSourceSchema,
+  type ExternalObjectCanonicalIdentityInput,
+  type ExternalObjectMentionSourceInput,
+  type ExternalObjectProviderKeyInput,
+  type ExternalObjectTypeInput,
+} from "./external-object.js";
 export {
   companySkillSourceTypeSchema,
   companySkillTrustLevelSchema,