feat: add cross-plugin secret references gated by the provider's RBAC permission

plugins/ai/backend/index.mjs

@@ -54,6 +54,28 @@ export async function activate(ctx) {
   routesModule = await loadRelative("routes");
   routesModule.startAiService();
 
+  // Offered by reference, not copied: this hands over a resolver, so the key
+  // stays ours. Rotating or deleting the provider takes effect on the next
+  // read by any borrower, and deactivate() below withdraws the offer entirely.
+  // The resolve is per-user because the keys are stored per-user and encrypted
+  // under that user's data key, so a borrowed read returns the acting user's
+  // own default key, never someone else's.
+  ctx.secrets.offer("api-key", async (userId) => {
+    const { createCurrentAiRepository } = await loadRelative(
+      "../../../backend/backend/database/repositories/factory",
+    );
+    const repository = createCurrentAiRepository();
+    const providers = await repository.listProviders(userId);
+    const preferred = providers.find((provider) => provider.apiKeyPrefix);
+    if (!preferred) return null;
+
+    const withSecret = await repository.findProviderWithSecret(
+      preferred.id,
+      userId,
+    );
+    return withSecret?.apiKey ?? null;
+  });
+
   ctx.log.info("AI assistant router registered at /ai");
 }
 

plugins/ai/manifest.json

@@ -31,7 +31,8 @@
         "ai.use",
         "ai.manage_providers",
         "ai.apply_proposals",
-        "ai.services.use"
+        "ai.services.use",
+        "ai.secrets.share"
       ],
       "defaultForRole": {
         "admin": ["ai.services.use"]
@@ -49,5 +50,12 @@
       }
     ]
   },
+  "providesSecret": [
+    {
+      "key": "api-key",
+      "permission": "ai.secrets.share",
+      "descriptionKey": "ai.secrets.shareApiKey"
+    }
+  ],
   "sidecars": []
 }

scripts/plugin-manifest.schema.json

@@ -331,6 +331,56 @@
         }
       }
     },
+    "providesSecret": {
+      "type": "array",
+      "description": "Secrets this plugin offers other plugins by reference. The value is never copied; a borrower re-reads it per call.",
+      "items": {
+        "type": "object",
+        "additionalProperties": false,
+        "required": ["key", "permission"],
+        "properties": {
+          "key": {
+            "type": "string",
+            "pattern": "^[a-z0-9-]+$",
+            "description": "Secret name within this plugin, e.g. \"api-key\"."
+          },
+          "permission": {
+            "type": "string",
+            "minLength": 1,
+            "description": "Role permission a borrowing user needs. Must also appear in contributes.permissionGroup.permissions."
+          },
+          "descriptionKey": {
+            "type": "string",
+            "minLength": 1,
+            "description": "i18n key describing the sharing, shown in the admin UI."
+          }
+        }
+      }
+    },
+    "requiresSecret": {
+      "type": "array",
+      "description": "Secrets this plugin borrows from another plugin. Reads resolve to null when the provider is absent or has nothing set.",
+      "items": {
+        "type": "object",
+        "additionalProperties": false,
+        "required": ["plugin", "key"],
+        "properties": {
+          "plugin": {
+            "type": "string",
+            "pattern": "^[a-z0-9-]+$",
+            "description": "Plugin id that offers the secret."
+          },
+          "key": {
+            "type": "string",
+            "pattern": "^[a-z0-9-]+$"
+          },
+          "optional": {
+            "type": "boolean",
+            "description": "When true, an absent provider is normal rather than reported as an unmet requirement."
+          }
+        }
+      }
+    },
     "sidecars": {
       "type": "array",
       "items": {

scripts/validate-plugin-manifest.cjs

@@ -18,6 +18,7 @@ const ID_PATTERN = /^[a-z0-9-]+$/;
 const SEMVER_PATTERN = /^\d+\.\d+\.\d+(-[0-9A-Za-z-.]+)?(\+[0-9A-Za-z-.]+)?$/;
 const API_VERSION_PATTERN = /^[0-9]+$/;
 const SERVICE_PATTERN = /^[a-z0-9-]+(\.[a-z0-9-]+)+$/;
+const SECRET_KEY_PATTERN = /^[a-z0-9-]+$/;
 // Dotted like a service name, but segments may be camelCase: these name a
 // frontend function ("ai.openWithContext"), not a lowercase service contract.
 const ACTION_ID_PATTERN = /^[a-z0-9-]+(\.[a-zA-Z0-9-]+)+$/;
@@ -132,6 +133,8 @@ function validateManifest(manifest, schema) {
 
   errors.push(...validateProvides(manifest.provides));
   errors.push(...validateRequires(manifest.requires));
+  errors.push(...validateProvidesSecret(manifest.providesSecret));
+  errors.push(...validateRequiresSecret(manifest.requiresSecret));
 
   if (manifest.contributes && typeof manifest.contributes === "object") {
     errors.push(...validateContributes(manifest.contributes));
@@ -150,6 +153,28 @@ function validateManifest(manifest, schema) {
     }
   }
 
+  // Same rule for a shared secret: sharing rides on the provider's own RBAC
+  // permission rather than a separate grant mechanism.
+  if (Array.isArray(manifest.providesSecret) && Array.isArray(declared)) {
+    for (const entry of manifest.providesSecret) {
+      if (entry && entry.permission && !declared.includes(entry.permission)) {
+        errors.push(
+          `Secret "${entry.key}" is gated by "${entry.permission}", which is not declared in contributes.permissionGroup.permissions`,
+        );
+      }
+    }
+  }
+
+  if (Array.isArray(manifest.requiresSecret)) {
+    for (const entry of manifest.requiresSecret) {
+      if (entry && entry.plugin && entry.plugin === manifest.id) {
+        errors.push(
+          `requiresSecret entry for "${entry.key}" names this plugin itself; use ctx.secrets.get instead`,
+        );
+      }
+    }
+  }
+
   // Same rule for UI actions: a permission the catalog never sees is one no
   // admin can grant, so the action would be invisible rather than denied.
   const actions = manifest.contributes?.actions;
@@ -257,6 +282,93 @@ function validateRequires(requires) {
   return errors;
 }
 
+function validateProvidesSecret(providesSecret) {
+  if (providesSecret === undefined) return [];
+  if (!Array.isArray(providesSecret)) {
+    return ['Field "providesSecret" must be an array'];
+  }
+
+  const errors = [];
+  const seen = new Set();
+
+  providesSecret.forEach((entry, index) => {
+    if (!entry || typeof entry !== "object" || Array.isArray(entry)) {
+      errors.push(`providesSecret[${index}] must be an object`);
+      return;
+    }
+
+    if (typeof entry.key !== "string" || !SECRET_KEY_PATTERN.test(entry.key)) {
+      errors.push(
+        `providesSecret[${index}].key must match ${SECRET_KEY_PATTERN}, got: "${entry.key}"`,
+      );
+    } else if (seen.has(entry.key)) {
+      errors.push(
+        `providesSecret[${index}].key is a duplicate: "${entry.key}"`,
+      );
+    } else {
+      seen.add(entry.key);
+    }
+
+    if (typeof entry.permission !== "string" || entry.permission.length === 0) {
+      errors.push(`providesSecret[${index}].permission is required`);
+    }
+
+    if (
+      "descriptionKey" in entry &&
+      (typeof entry.descriptionKey !== "string" ||
+        entry.descriptionKey.length === 0)
+    ) {
+      errors.push(`providesSecret[${index}].descriptionKey must be a string`);
+    }
+  });
+
+  return errors;
+}
+
+function validateRequiresSecret(requiresSecret) {
+  if (requiresSecret === undefined) return [];
+  if (!Array.isArray(requiresSecret)) {
+    return ['Field "requiresSecret" must be an array'];
+  }
+
+  const errors = [];
+  const seen = new Set();
+
+  requiresSecret.forEach((entry, index) => {
+    if (!entry || typeof entry !== "object" || Array.isArray(entry)) {
+      errors.push(`requiresSecret[${index}] must be an object`);
+      return;
+    }
+
+    if (typeof entry.plugin !== "string" || !ID_PATTERN.test(entry.plugin)) {
+      errors.push(
+        `requiresSecret[${index}].plugin must match ${ID_PATTERN}, got: "${entry.plugin}"`,
+      );
+    }
+
+    if (typeof entry.key !== "string" || !SECRET_KEY_PATTERN.test(entry.key)) {
+      errors.push(
+        `requiresSecret[${index}].key must match ${SECRET_KEY_PATTERN}, got: "${entry.key}"`,
+      );
+    }
+
+    if (typeof entry.plugin === "string" && typeof entry.key === "string") {
+      const id = `${entry.plugin}:${entry.key}`;
+      if (seen.has(id)) {
+        errors.push(`requiresSecret[${index}] is a duplicate: "${id}"`);
+      } else {
+        seen.add(id);
+      }
+    }
+
+    if ("optional" in entry && typeof entry.optional !== "boolean") {
+      errors.push(`requiresSecret[${index}].optional must be a boolean`);
+    }
+  });
+
+  return errors;
+}
+
 function validateContributes(contributes) {
   const errors = [];
 

src/backend/plugins/host-ctx.ts

@@ -19,6 +19,8 @@ import { pluginEvents } from "./events.js";
 import * as registry from "./registry.js";
 import * as serviceRegistry from "./service-registry.js";
 import type { ServiceRegistration } from "./service-registry.js";
+import * as secretRegistry from "./secret-registry.js";
+import type { SecretRegistration } from "./secret-registry.js";
 import { safeDetails } from "./broker.js";
 import type { PluginManifest } from "./manifest.js";
 
@@ -58,6 +60,26 @@ export interface InProcessPluginContext {
       options?: { userId?: string },
     ) => T;
   };
+  /**
+   * Secrets shared between plugins by reference.
+   *
+   * `offer` publishes a resolver, never a value, so the provider keeps the
+   * ability to rotate or clear it at any time. `getShared` reads another
+   * plugin's offered secret for one call, gated by that provider's own role
+   * permission. See secret-registry.ts.
+   */
+  secrets: {
+    offer: (
+      key: string,
+      resolve: (userId: string) => Promise<string | null> | string | null,
+    ) => void;
+    withdraw: (key: string) => boolean;
+    getShared: (
+      pluginId: string,
+      key: string,
+      options?: { userId?: string },
+    ) => Promise<string | null>;
+  };
 }
 
 /**
@@ -73,6 +95,8 @@ export interface InProcessHandle {
   providedKeys: Array<{ key: string; value: unknown }>;
   /** Declared services this plugin provided, revoked on deactivate. */
   providedServices: ServiceRegistration[];
+  /** Shared secrets this plugin offered, withdrawn on deactivate. */
+  offeredSecrets: SecretRegistration[];
 }
 
 export interface PluginModule {
@@ -180,20 +204,61 @@ export function createInProcessContext(
       get: (service, options) =>
         serviceRegistry.createServiceHandle(service, pluginId, {
           resolveUserId: () => options?.userId,
-          hasPermission: async (userId, permission) => {
-            const { PermissionManager } =
-              await import("../utils/permission-manager.js");
-            return PermissionManager.getInstance().hasPermission(
-              userId,
-              permission,
-            );
-          },
+          hasPermission: checkPermission,
           audit: (entry) => writeServiceAudit(entry),
         }),
     },
+
+    secrets: {
+      offer: (key, resolve) => {
+        // Declared AND offered, the same rule services.provide enforces.
+        const declared = manifest.providesSecret?.find(
+          (entry) => entry.key === key,
+        );
+        if (!declared) {
+          throw new Error(
+            `Plugin ${pluginId} cannot offer secret "${key}": it is not declared in the manifest's providesSecret array`,
+          );
+        }
+
+        const registration = secretRegistry.offerSecret({
+          pluginId,
+          pluginName: manifest.name,
+          key,
+          permission: declared.permission,
+          resolve,
+        });
+        handle.offeredSecrets.push(registration);
+      },
+
+      withdraw: (key) => {
+        const registration = handle.offeredSecrets.find(
+          (entry) => entry.key === key,
+        );
+        handle.offeredSecrets = handle.offeredSecrets.filter(
+          (entry) => entry !== registration,
+        );
+        return secretRegistry.withdrawSecret(pluginId, key, registration);
+      },
+
+      getShared: (providerPluginId, key, options) =>
+        secretRegistry.readSharedSecret(manifest, providerPluginId, key, {
+          resolveUserId: () => options?.userId,
+          hasPermission: checkPermission,
+          audit: (entry) => writeSecretAudit(entry),
+        }),
+    },
   };
 }
 
+async function checkPermission(
+  userId: string,
+  permission: string,
+): Promise<boolean> {
+  const { PermissionManager } = await import("../utils/permission-manager.js");
+  return PermissionManager.getInstance().hasPermission(userId, permission);
+}
+
 /**
  * Mirrors PluginBroker.audit: attribution comes from the runtime, never from
  * the plugin, and the details only ever record the shape of a call.
@@ -222,6 +287,35 @@ async function writeServiceAudit(
   }
 }
 
+/**
+ * Records that a secret was borrowed, never what it was.
+ *
+ * `resolved` is the only thing said about the value: whether one came back at
+ * all. That is what makes the trail useful (you can see a consumer running on
+ * someone else's key) without the trail itself becoming a place the secret
+ * leaks to.
+ */
+async function writeSecretAudit(
+  entry: secretRegistry.SecretAuditEntry,
+): Promise<void> {
+  try {
+    const { logAudit } = await import("../utils/audit-logger.js");
+    await logAudit({
+      userId: entry.userId,
+      username: `plugin:${entry.consumerPluginId}`,
+      action: "plugin_secret_shared_read",
+      resourceType: "plugin",
+      resourceId: entry.providerPluginId,
+      resourceName: entry.providerPluginName,
+      details: `${entry.consumerPluginId} read shared secret "${entry.providerPluginId}:${entry.key}" (resolved: ${entry.resolved})`,
+      success: entry.success,
+      errorMessage: entry.errorMessage,
+    });
+  } catch {
+    // Auditing must never break the caller.
+  }
+}
+
 /** Undoes everything the ctx handed out. Safe to call more than once. */
 export async function disposeInProcessHandle(
   handle: InProcessHandle,
@@ -239,6 +333,21 @@ export async function disposeInProcessHandle(
   }
   handle.providedServices = [];
 
+  // Withdrawing the offers is what turns a borrower's getShared into a plain
+  // null instead of a handle pointing at a resolver whose plugin is gone. The
+  // sweep afterwards is belt and braces: an offer made outside the ctx, or one
+  // whose push was lost to a crash mid-activate, would otherwise outlive the
+  // plugin that backs it.
+  for (const registration of handle.offeredSecrets) {
+    secretRegistry.withdrawSecret(
+      registration.pluginId,
+      registration.key,
+      registration,
+    );
+  }
+  handle.offeredSecrets = [];
+  secretRegistry.withdrawAllForPlugin(pluginId);
+
   for (const unsubscribe of handle.unsubscribers) {
     try {
       unsubscribe();

src/backend/plugins/loader.ts

@@ -55,6 +55,10 @@ import {
   type PluginModule,
 } from "./host-ctx.js";
 import { resolveRequirements } from "./service-registry.js";
+import {
+  resolveSecretRequirements,
+  withdrawAllForPlugin,
+} from "./secret-registry.js";
 
 export type PluginState =
   | "loaded"
@@ -361,11 +365,25 @@ export class PluginLoader {
         );
       }
 
+      // Secret references never block activation, even when not optional. A
+      // borrowed secret is resolved per call and returns null when absent, so
+      // a provider installed later starts working with no restart -- refusing
+      // to start here would turn a recoverable gap into a hard ordering
+      // dependency between two installs.
+      const secretResolution = resolveSecretRequirements(plugin.manifest);
+      for (const reference of secretResolution.unavailable) {
+        pluginLogger.info(
+          `Plugin ${plugin.id} shared secret "${reference}" is not currently offered; reads will resolve to null`,
+          { operation: "plugin_activate" },
+        );
+      }
+
       const handle: InProcessHandle = {
         module: { activate, deactivate },
         unsubscribers: [],
         providedKeys: [],
         providedServices: [],
+        offeredSecrets: [],
       };
 
       const ctx = createInProcessContext(plugin.manifest, handle);
@@ -576,6 +594,11 @@ export class PluginLoader {
       return;
     }
 
+    // A worker plugin cannot offer a shared secret today, but terminate() is
+    // the one path every tier goes through, so the sweep belongs here rather
+    // than only in the in-process branch above.
+    withdrawAllForPlugin(plugin.id);
+
     const worker = plugin.worker;
     if (!worker) return;
 

src/backend/plugins/manifest.ts

@@ -81,6 +81,12 @@ const API_VERSION_PATTERN = /^[0-9]+$/;
 const API_PREFIX_PATTERN = /^[a-z0-9-]+$/;
 /** Service names are dotted, e.g. "ssh.transport" or "host-metrics.stream". */
 const SERVICE_PATTERN = /^[a-z0-9-]+(\.[a-z0-9-]+)+$/;
+/**
+ * A shared secret key is a flat slug, e.g. "api-key". Not dotted: the plugin
+ * id is already a separate field, so a dotted key would only invite encoding
+ * the owner twice and disagreeing with itself.
+ */
+const SECRET_KEY_PATTERN = /^[a-z0-9-]+$/;
 /**
  * Action and slot ids are dotted like service names, but each segment may be
  * camelCase: these name a frontend function ("ai.openWithContext"), not a
@@ -145,6 +151,13 @@ export interface PluginManifest {
   provides?: PluginServiceProvide[];
   /** Named services this plugin needs another active plugin to provide. */
   requires?: PluginServiceRequire[];
+  /**
+   * Secrets this plugin offers other plugins by reference. Gated by one of
+   * this plugin's own permissionGroup permissions -- see parseManifest.
+   */
+  providesSecret?: PluginSecretProvide[];
+  /** Secrets this plugin wants to borrow from another plugin, by reference. */
+  requiresSecret?: PluginSecretRequire[];
   sidecars: Array<{ id: string; binary: string }>;
 }
 
@@ -162,6 +175,28 @@ export interface PluginServiceRequire {
   optional?: boolean;
 }
 
+export interface PluginSecretProvide {
+  /** The secret's name within this plugin, e.g. "api-key". */
+  key: string;
+  /** The role permission a borrowing user needs. */
+  permission: string;
+  /** Shown in the admin UI so the sharing is legible without reading code. */
+  descriptionKey?: string;
+}
+
+export interface PluginSecretRequire {
+  /** The plugin id that offers the secret. */
+  plugin: string;
+  /** The secret's name within that plugin. */
+  key: string;
+  /**
+   * When true, the provider being absent is normal and activation proceeds.
+   * A non-optional reference still activates -- the read just returns null --
+   * but resolveSecretRequirements reports it as an error for install feedback.
+   */
+  optional?: boolean;
+}
+
 /**
  * A named frontend action, declared here and bound at runtime.
  *
@@ -300,6 +335,8 @@ export function validateManifest(manifest: unknown): string[] {
 
   errors.push(...validateProvides(m.provides));
   errors.push(...validateRequires(m.requires));
+  errors.push(...validateProvidesSecret(m.providesSecret));
+  errors.push(...validateRequiresSecret(m.requiresSecret));
 
   if (m.contributes && typeof m.contributes === "object") {
     errors.push(
@@ -389,6 +426,92 @@ function validateRequires(requires: unknown): string[] {
   return errors;
 }
 
+function validateProvidesSecret(providesSecret: unknown): string[] {
+  if (providesSecret === undefined) return [];
+  if (!Array.isArray(providesSecret)) {
+    return ['Field "providesSecret" must be an array'];
+  }
+
+  const errors: string[] = [];
+  const seen = new Set<string>();
+
+  providesSecret.forEach((entry: unknown, index: number) => {
+    if (!entry || typeof entry !== "object" || Array.isArray(entry)) {
+      errors.push(`providesSecret[${index}] must be an object`);
+      return;
+    }
+    const e = entry as Record<string, unknown>;
+
+    if (typeof e.key !== "string" || !SECRET_KEY_PATTERN.test(e.key)) {
+      errors.push(
+        `providesSecret[${index}].key must match ${SECRET_KEY_PATTERN}, got: "${String(e.key)}"`,
+      );
+    } else if (seen.has(e.key)) {
+      errors.push(`providesSecret[${index}].key is a duplicate: "${e.key}"`);
+    } else {
+      seen.add(e.key);
+    }
+
+    if (typeof e.permission !== "string" || e.permission.length === 0) {
+      errors.push(`providesSecret[${index}].permission is required`);
+    }
+
+    if (
+      "descriptionKey" in e &&
+      (typeof e.descriptionKey !== "string" || e.descriptionKey.length === 0)
+    ) {
+      errors.push(`providesSecret[${index}].descriptionKey must be a string`);
+    }
+  });
+
+  return errors;
+}
+
+function validateRequiresSecret(requiresSecret: unknown): string[] {
+  if (requiresSecret === undefined) return [];
+  if (!Array.isArray(requiresSecret)) {
+    return ['Field "requiresSecret" must be an array'];
+  }
+
+  const errors: string[] = [];
+  const seen = new Set<string>();
+
+  requiresSecret.forEach((entry: unknown, index: number) => {
+    if (!entry || typeof entry !== "object" || Array.isArray(entry)) {
+      errors.push(`requiresSecret[${index}] must be an object`);
+      return;
+    }
+    const e = entry as Record<string, unknown>;
+
+    if (typeof e.plugin !== "string" || !ID_PATTERN.test(e.plugin)) {
+      errors.push(
+        `requiresSecret[${index}].plugin must match ${ID_PATTERN}, got: "${String(e.plugin)}"`,
+      );
+    }
+
+    if (typeof e.key !== "string" || !SECRET_KEY_PATTERN.test(e.key)) {
+      errors.push(
+        `requiresSecret[${index}].key must match ${SECRET_KEY_PATTERN}, got: "${String(e.key)}"`,
+      );
+    }
+
+    if (typeof e.plugin === "string" && typeof e.key === "string") {
+      const id = `${e.plugin}:${e.key}`;
+      if (seen.has(id)) {
+        errors.push(`requiresSecret[${index}] is a duplicate: "${id}"`);
+      } else {
+        seen.add(id);
+      }
+    }
+
+    if ("optional" in e && typeof e.optional !== "boolean") {
+      errors.push(`requiresSecret[${index}].optional must be a boolean`);
+    }
+  });
+
+  return errors;
+}
+
 function validateContributes(contributes: Record<string, unknown>): string[] {
   const errors: string[] = [];
 
@@ -644,6 +767,32 @@ export function parseManifest(raw: unknown): {
     }
   }
 
+  // Same rule for a shared secret. This is what keeps sharing on the existing
+  // RBAC grant path instead of becoming a separate mechanism: the permission
+  // gating a borrowed secret is an ordinary role permission in the provider's
+  // own group, editable per role or per user like any other.
+  for (const entry of manifest.providesSecret ?? []) {
+    if (!declaredPermissions.includes(entry.permission)) {
+      return {
+        errors: [
+          `Secret "${entry.key}" is gated by "${entry.permission}", which is not declared in contributes.permissionGroup.permissions`,
+        ],
+      };
+    }
+  }
+
+  // A plugin borrowing from itself would bypass nothing, but it is always a
+  // mistake: its own secrets are reachable through ctx.secrets directly.
+  for (const entry of manifest.requiresSecret ?? []) {
+    if (entry.plugin === manifest.id) {
+      return {
+        errors: [
+          `requiresSecret entry for "${entry.key}" names this plugin itself; use ctx.secrets.get instead`,
+        ],
+      };
+    }
+  }
+
   // Same rule for UI actions, for the same reason: a permission the catalog
   // never sees is one no admin can grant, so the action would be invisible
   // forever rather than merely denied.

src/backend/plugins/secret-registry.ts

@@ -0,0 +1,362 @@
+/**
+ * Cross-plugin secret references.
+ *
+ * A plugin that holds a secret (the AI assistant and its provider API key) can
+ * offer it to other plugins by name, without ever handing over a copy. A
+ * requiring plugin declares `requiresSecret` in its manifest and calls
+ * ctx.secrets.getShared(pluginId, key) per request; the value is resolved from
+ * the provider at that moment and returned for that one call.
+ *
+ * ## Why a resolver and not a stored value
+ *
+ * The registration holds a `resolve` callback owned by the providing plugin,
+ * never the secret itself. That is the whole point of the design:
+ *
+ *   - The provider can rotate or clear the underlying secret at any time. The
+ *     next getShared() runs the new resolver and sees the new value, with no
+ *     invalidation step to forget and no cached copy to go stale.
+ *   - There is nothing for the requiring plugin to persist. It gets a string
+ *     back from one call. It could of course write that string somewhere
+ *     itself, exactly as it could with any value it is legitimately given --
+ *     what it cannot do is hold a handle that keeps working after the provider
+ *     revokes, because every call re-resolves through the provider.
+ *   - Uninstalling the provider deletes the registration, so every later
+ *     getShared() returns null rather than throwing on a dangling handle. A
+ *     missing dependency is a normal condition here, unlike a service call,
+ *     which is why this returns null instead of the service registry's
+ *     PluginServiceUnavailableError.
+ *
+ * ## Authorization is the provider's own permission
+ *
+ * No fourth grant mechanism. The provider declares which of its own role
+ * permissions gates sharing ("ai.secrets.share", alongside "ai.services.use"),
+ * and getShared runs the acting user through the same PermissionManager check
+ * that service-registry.ts and requirePermission() use. So:
+ *
+ *   - An admin can let one user's requests reuse the shared key and deny
+ *     another's, purely in the role editor, with no reinstall.
+ *   - Revoking the RBAC permission takes effect on the very next call, exactly
+ *     like revoking the secret itself.
+ *   - The check is per-user and per-call, while `requiresSecret` in the
+ *     manifest is per-install. They are independent on purpose: whether the
+ *     plugin may ask is a deploy-time decision, whether this user's request
+ *     gets a value is a runtime one.
+ *
+ * A denial is an error (the caller asked for something it is not allowed to
+ * have), while an absent secret is null (the caller asked for something that
+ * legitimately is not there). Collapsing the two would let a consumer treat
+ * "you may not" as "not configured" and fall back to something weaker.
+ */
+
+import { pluginLogger } from "../utils/logger.js";
+import type { PluginManifest, PluginSecretRequire } from "./manifest.js";
+
+export interface SecretRegistration {
+  /** The plugin offering the secret. */
+  pluginId: string;
+  /** Display name, for audit lines. */
+  pluginName: string;
+  /** The secret's name within that plugin, e.g. "api-key". */
+  key: string;
+  /** Role permission the acting user needs. Declared by the provider. */
+  permission: string;
+  /**
+   * Returns the current value, or null when the provider has nothing set.
+   * Called on every read so a rotation is picked up with no invalidation.
+   */
+  resolve: (userId: string) => Promise<string | null> | string | null;
+  /** Bumped on every offer, so a re-registered provider invalidates nothing stale. */
+  generation: number;
+}
+
+/** Keyed by `${pluginId}:${key}`. */
+const secrets = new Map<string, SecretRegistration>();
+let generationCounter = 0;
+
+function mapKey(pluginId: string, key: string): string {
+  return `${pluginId}:${key}`;
+}
+
+/**
+ * Thrown when the acting user lacks the provider's sharing permission.
+ *
+ * Mirrors PluginServicePermissionError: `status` and `body` are the 403 shape
+ * requirePermission() sends, so a consumer serving an HTTP request can pass it
+ * straight through.
+ */
+export class PluginSecretPermissionError extends Error {
+  readonly code = "EPLUGINSECRETPERM";
+  readonly status = 403;
+  readonly body: { error: string; required: string };
+
+  constructor(pluginId: string, key: string, permission: string) {
+    super(
+      `You do not have access to the "${key}" secret shared by "${pluginId}". ` +
+        `It requires the "${permission}" permission.`,
+    );
+    this.name = "PluginSecretPermissionError";
+    this.body = { error: "Insufficient permissions", required: permission };
+  }
+}
+
+/** Thrown when a read cannot be attributed to a user. */
+export class PluginSecretActorError extends Error {
+  readonly code = "EPLUGINSECRETACTOR";
+
+  constructor(pluginId: string, key: string) {
+    super(
+      `A read of "${pluginId}:${key}" has no acting user. Pass one with ` +
+        `ctx.secrets.forUser(userId).getShared(...).`,
+    );
+    this.name = "PluginSecretActorError";
+  }
+}
+
+/** Thrown when a plugin asks for a secret its manifest never declared. */
+export class PluginSecretUndeclaredError extends Error {
+  readonly code = "EPLUGINSECRETUNDECLARED";
+
+  constructor(consumerPluginId: string, pluginId: string, key: string) {
+    super(
+      `Plugin ${consumerPluginId} cannot read "${pluginId}:${key}": it is not ` +
+        `declared in the manifest's requiresSecret array`,
+    );
+    this.name = "PluginSecretUndeclaredError";
+  }
+}
+
+export function offerSecret(
+  registration: Omit<SecretRegistration, "generation">,
+): SecretRegistration {
+  const id = mapKey(registration.pluginId, registration.key);
+  const existing = secrets.get(id);
+  if (existing) {
+    pluginLogger.warn(
+      `Shared secret "${id}" is already offered and is being replaced`,
+      { operation: "plugin_secret_registry" },
+    );
+  }
+
+  const entry: SecretRegistration = {
+    ...registration,
+    generation: ++generationCounter,
+  };
+  secrets.set(id, entry);
+  return entry;
+}
+
+/**
+ * Withdraws an offer, identity-checked like revokeService: a provider that
+ * crashed and restarted must not withdraw the replacement its own restart
+ * installed.
+ *
+ * Nothing is remembered afterwards. A service keeps a tombstone so a held
+ * handle throws a named error, but a secret reference has no handle to keep
+ * alive -- the next read simply finds nothing and returns null.
+ */
+export function withdrawSecret(
+  pluginId: string,
+  key: string,
+  registration?: SecretRegistration,
+): boolean {
+  const id = mapKey(pluginId, key);
+  const current = secrets.get(id);
+  if (!current) return false;
+  if (registration && current.generation !== registration.generation) {
+    return false;
+  }
+  return secrets.delete(id);
+}
+
+/** Withdraws every offer made by one plugin. Used when it is uninstalled. */
+export function withdrawAllForPlugin(pluginId: string): number {
+  let removed = 0;
+  for (const [id, registration] of secrets) {
+    if (registration.pluginId === pluginId) {
+      secrets.delete(id);
+      removed++;
+    }
+  }
+  return removed;
+}
+
+export function getSecretRegistration(
+  pluginId: string,
+  key: string,
+): SecretRegistration | undefined {
+  return secrets.get(mapKey(pluginId, key));
+}
+
+export function listSecrets(): SecretRegistration[] {
+  return [...secrets.values()];
+}
+
+/** Test seam. */
+export function clearSecretRegistry(): void {
+  secrets.clear();
+}
+
+export interface SecretRequirementResolution {
+  /** Declared requirements whose provider is present and has a value offered. */
+  available: string[];
+  /** Declared requirements with no matching offer right now. */
+  unavailable: string[];
+  /** Human-readable reasons for each unsatisfied non-optional requirement. */
+  errors: string[];
+}
+
+/**
+ * Structural resolution of a manifest's `requiresSecret`.
+ *
+ * Like resolveRequirements in service-registry.ts, this deliberately does NOT
+ * consult any user's permissions: activation is per-instance, permissions are
+ * per-user. It only asks whether the named plugin currently offers the key.
+ *
+ * Availability here is a snapshot for logging and install-time feedback. It is
+ * never cached into the call path -- getShared re-resolves every time, so a
+ * provider that appears after activation starts working with no restart.
+ */
+export function resolveSecretRequirements(
+  manifest: PluginManifest,
+): SecretRequirementResolution {
+  const available: string[] = [];
+  const unavailable: string[] = [];
+  const errors: string[] = [];
+
+  for (const requirement of manifest.requiresSecret ?? []) {
+    const id = mapKey(requirement.plugin, requirement.key);
+    if (secrets.has(id)) {
+      available.push(id);
+      continue;
+    }
+
+    unavailable.push(id);
+    if (!requirement.optional) {
+      errors.push(
+        `requires secret "${requirement.key}" from plugin "${requirement.plugin}", which is not currently offered`,
+      );
+    }
+  }
+
+  return { available, unavailable, errors };
+}
+
+export interface SecretReadContext {
+  /** Resolves the user this read acts as. */
+  resolveUserId: () => string | undefined;
+  /** Checks a role permission for a user. */
+  hasPermission: (userId: string, permission: string) => Promise<boolean>;
+  /** Writes the audit line. Must never throw. Awaited before the value returns. */
+  audit: (entry: SecretAuditEntry) => void | Promise<void>;
+}
+
+export interface SecretAuditEntry {
+  userId: string;
+  consumerPluginId: string;
+  providerPluginId: string;
+  providerPluginName: string;
+  key: string;
+  /** False for a denial, true for an allowed read whether or not a value existed. */
+  success: boolean;
+  /** Whether a value actually came back. Never the value itself. */
+  resolved: boolean;
+  errorMessage?: string;
+}
+
+/**
+ * Reads a shared secret for one call.
+ *
+ * Returns null, rather than throwing, when the provider is not installed or
+ * has nothing set. Those are ordinary conditions a consumer is expected to
+ * handle (fall back to its own key, or tell the user to configure one), and an
+ * optional dependency that threw would force every consumer to wrap each read.
+ *
+ * Throws only for the two cases that are genuinely wrong: a plugin reading
+ * something its manifest never declared, and a user without the permission.
+ */
+export async function readSharedSecret(
+  consumerManifest: PluginManifest,
+  providerPluginId: string,
+  key: string,
+  context: SecretReadContext,
+): Promise<string | null> {
+  const consumerPluginId = consumerManifest.id;
+
+  // Declared in the manifest, the same rule services.provide enforces: a
+  // plugin cannot reach a secret it never asked for, even if an admin granted
+  // the permission for some other reason.
+  const declared = (consumerManifest.requiresSecret ?? []).find(
+    (entry: PluginSecretRequire) =>
+      entry.plugin === providerPluginId && entry.key === key,
+  );
+  if (!declared) {
+    throw new PluginSecretUndeclaredError(
+      consumerPluginId,
+      providerPluginId,
+      key,
+    );
+  }
+
+  const registration = secrets.get(mapKey(providerPluginId, key));
+
+  // Provider absent: uninstalled, disabled, or never installed. Indistinguish-
+  // able on purpose, and all four are the same answer to the consumer -- which
+  // is also what makes an uninstall clean rather than a dangling handle.
+  if (!registration) return null;
+
+  const userId = context.resolveUserId();
+  if (!userId) {
+    throw new PluginSecretActorError(providerPluginId, key);
+  }
+
+  const allowed = await context.hasPermission(userId, registration.permission);
+  if (!allowed) {
+    const error = new PluginSecretPermissionError(
+      providerPluginId,
+      key,
+      registration.permission,
+    );
+    await context.audit({
+      userId,
+      consumerPluginId,
+      providerPluginId: registration.pluginId,
+      providerPluginName: registration.pluginName,
+      key,
+      success: false,
+      resolved: false,
+      errorMessage: error.message,
+    });
+    throw error;
+  }
+
+  try {
+    const value = await registration.resolve(userId);
+    const resolved = typeof value === "string" && value.length > 0;
+
+    await context.audit({
+      userId,
+      consumerPluginId,
+      providerPluginId: registration.pluginId,
+      providerPluginName: registration.pluginName,
+      key,
+      success: true,
+      resolved,
+    });
+
+    return resolved ? value : null;
+  } catch (error) {
+    await context.audit({
+      userId,
+      consumerPluginId,
+      providerPluginId: registration.pluginId,
+      providerPluginName: registration.pluginName,
+      key,
+      success: false,
+      resolved: false,
+      errorMessage: error instanceof Error ? error.message : String(error),
+    });
+    // A provider whose own lookup failed is not a permission problem, and the
+    // consumer should not read it as "not configured" and fall back.
+    throw error;
+  }
+}

src/backend/plugins/worker-bootstrap.ts

@@ -256,6 +256,12 @@ const ctx = {
   secrets: {
     get: notImplemented("secrets.get"),
     set: notImplemented("secrets.set"),
+    // Cross-plugin sharing is in-process only for now. Named here rather than
+    // left undefined so a worker plugin that tries it gets the same explicit
+    // error as any other unimplemented ctx call.
+    offer: notImplemented("secrets.offer"),
+    withdraw: notImplemented("secrets.withdraw"),
+    getShared: notImplemented("secrets.getShared"),
   },
   notify: notImplemented("notify"),
   fetch: notImplemented("fetch"),

src/backend/tests/plugins/manifest.test.ts

@@ -150,6 +150,116 @@ describe("plugin manifest validation", () => {
     });
   });
 
+  describe("providesSecret / requiresSecret", () => {
+    const permissionGroup = {
+      group: "testplugin",
+      permissions: ["testplugin.secrets.share"],
+    };
+
+    it("accepts a well-formed pair", () => {
+      expect(
+        validateManifest(
+          validManifest({
+            providesSecret: [
+              { key: "api-key", permission: "testplugin.secrets.share" },
+            ],
+            requiresSecret: [
+              { plugin: "ai-assistant", key: "api-key", optional: true },
+            ],
+            contributes: { permissionGroup },
+          }),
+        ),
+      ).toEqual([]);
+    });
+
+    it("rejects a dotted secret key", () => {
+      // The owning plugin is already its own field, so a dotted key would only
+      // encode the owner twice and invite the two disagreeing.
+      const errors = validateManifest(
+        validManifest({
+          providesSecret: [
+            { key: "ai.api-key", permission: "testplugin.secrets.share" },
+          ],
+        }),
+      );
+      expect(errors.some((e) => e.includes("providesSecret[0].key"))).toBe(
+        true,
+      );
+    });
+
+    it("rejects a duplicate offer of the same key", () => {
+      const errors = validateManifest(
+        validManifest({
+          providesSecret: [
+            { key: "api-key", permission: "testplugin.secrets.share" },
+            { key: "api-key", permission: "testplugin.secrets.share" },
+          ],
+        }),
+      );
+      expect(errors.some((e) => e.includes("duplicate"))).toBe(true);
+    });
+
+    it("requires a permission on an offer", () => {
+      const errors = validateManifest(
+        validManifest({ providesSecret: [{ key: "api-key" }] }),
+      );
+      expect(
+        errors.some((e) => e.includes("providesSecret[0].permission")),
+      ).toBe(true);
+    });
+
+    it("rejects a reference with a bad plugin id", () => {
+      const errors = validateManifest(
+        validManifest({
+          requiresSecret: [{ plugin: "Bad_Id", key: "api-key" }],
+        }),
+      );
+      expect(errors.some((e) => e.includes("requiresSecret[0].plugin"))).toBe(
+        true,
+      );
+    });
+
+    it("rejects a duplicate reference to the same plugin and key", () => {
+      const errors = validateManifest(
+        validManifest({
+          requiresSecret: [
+            { plugin: "ai-assistant", key: "api-key" },
+            { plugin: "ai-assistant", key: "api-key" },
+          ],
+        }),
+      );
+      expect(errors.some((e) => e.includes("duplicate"))).toBe(true);
+    });
+
+    it("refuses a shared secret gated by a permission the group never declares", () => {
+      // Same rule as a service: sharing rides on an ordinary role permission,
+      // so it has to be one an admin can actually grant.
+      const { manifest, errors } = parseManifest(
+        validManifest({
+          providesSecret: [
+            { key: "api-key", permission: "testplugin.undeclared" },
+          ],
+          contributes: { permissionGroup },
+        }),
+      );
+
+      expect(manifest).toBeUndefined();
+      expect(errors[0]).toContain("testplugin.undeclared");
+      expect(errors[0]).toContain("permissionGroup");
+    });
+
+    it("refuses a plugin borrowing from itself", () => {
+      const { manifest, errors } = parseManifest(
+        validManifest({
+          requiresSecret: [{ plugin: "sample-plugin", key: "api-key" }],
+        }),
+      );
+
+      expect(manifest).toBeUndefined();
+      expect(errors[0]).toContain("names this plugin itself");
+    });
+  });
+
   it("rejects an unknown permission", () => {
     const errors = validateManifest(
       validManifest({ permissions: ["credentials.read"] }),

src/backend/tests/plugins/secret-contract.test.ts

@@ -0,0 +1,394 @@
+/**
+ * Two real plugins on disk, one offering a secret and one borrowing it, driven
+ * through the actual PluginLoader.
+ *
+ * Same borrowed-id trick as service-contract.test.ts: the in-process allowlist
+ * is hardcoded and deliberately unfakeable, so the fixtures use real
+ * first-party ids to reach that tier. The secret ("api-key") and the
+ * permission gating it ("testplugin.secrets.share") are fixture-owned, so
+ * nothing about the shipped ssh-terminal or docker plugins is under test.
+ *
+ * What the unit test cannot show, and this does: that the manifest declaration
+ * is enforced by the real ctx, and that a genuine uninstall through
+ * loader.deactivate() leaves the borrower with null rather than a handle onto
+ * a resolver whose plugin is gone.
+ */
+
+import { afterEach, beforeEach, describe, expect, it, vi } from "vitest";
+import fs from "node:fs";
+import path from "node:path";
+import type { Fixture } from "./fixture-plugin.js";
+
+const state = vi.hoisted(() => ({
+  /** Permissions the acting user currently holds. Mutated mid-test. */
+  granted: new Set<string>(),
+  auditEntries: [] as Record<string, unknown>[],
+}));
+
+vi.mock("../../utils/logger.js", () => ({
+  pluginLogger: {
+    debug: vi.fn(),
+    info: vi.fn(),
+    warn: vi.fn(),
+    error: vi.fn(),
+    success: vi.fn(),
+  },
+}));
+
+vi.mock("../../utils/audit-logger.js", () => ({
+  logAudit: vi.fn(async (params: Record<string, unknown>) => {
+    state.auditEntries.push(params);
+  }),
+  getAuditUsername: vi.fn(async (userId: string) => `user:${userId}`),
+}));
+
+vi.mock("../../utils/permission-manager.js", () => ({
+  PermissionManager: {
+    getInstance: () => ({
+      hasPermission: async (_userId: string, permission: string) =>
+        state.granted.has(permission),
+      invalidateUserPermissionCache: vi.fn(),
+    }),
+  },
+}));
+
+const { PluginLoader } = await import("../../plugins/loader.js");
+const { TRANSPORT_OWNER_CAPABILITY } =
+  await import("../../plugins/first-party.js");
+const {
+  clearSecretRegistry,
+  getSecretRegistration,
+  PluginSecretPermissionError,
+  PluginSecretUndeclaredError,
+} = await import("../../plugins/secret-registry.js");
+const { pluginEvents } = await import("../../plugins/events.js");
+const { createFixturePlugin } = await import("./fixture-plugin.js");
+
+const PROVIDER_ID = "ssh-terminal";
+const CONSUMER_ID = "docker";
+const KEY = "api-key";
+const PERMISSION = "testplugin.secrets.share";
+const SECRET = "sk-fixture-value";
+
+/**
+ * The provider offers a resolver reading the current value from a file, so the
+ * test can rotate or clear it from outside without restarting the plugin. A
+ * module-level variable would not work: the plugin is imported by URL and
+ * lives in its own ESM module instance.
+ */
+function providerSource(valueFile: string): string {
+  const literal = JSON.stringify(valueFile);
+  return `
+import fs from "node:fs";
+export async function activate(ctx) {
+  ctx.secrets.offer(${JSON.stringify(KEY)}, async () => {
+    if (!fs.existsSync(${literal})) return null;
+    const value = fs.readFileSync(${literal}, "utf8");
+    return value.length > 0 ? value : null;
+  });
+}
+`;
+}
+
+/**
+ * The consumer stashes a bound read on globalThis so the test can invoke it as
+ * a specific user afterwards. Note it stashes a FUNCTION, not a value: there
+ * is no handle to hold, which is the property under test.
+ */
+const CONSUMER_SOURCE = `
+export async function activate(ctx) {
+  globalThis.__borrow = (userId) =>
+    ctx.secrets.getShared(${JSON.stringify(PROVIDER_ID)}, ${JSON.stringify(KEY)}, { userId });
+  globalThis.__borrowUndeclared = (userId) =>
+    ctx.secrets.getShared(${JSON.stringify(PROVIDER_ID)}, "not-declared", { userId });
+}
+`;
+
+function providerFixture(): Fixture {
+  return createFixturePlugin({
+    id: PROVIDER_ID,
+    permissions: [TRANSPORT_OWNER_CAPABILITY],
+    manifestOverrides: {
+      category: "Terminal",
+      providesSecret: [{ key: KEY, permission: PERMISSION }],
+      contributes: {
+        permissionGroup: { group: "testplugin", permissions: [PERMISSION] },
+      },
+    },
+  });
+}
+
+function consumerFixture(
+  requiresSecret: Array<Record<string, unknown>> = [
+    { plugin: PROVIDER_ID, key: KEY, optional: true },
+  ],
+): Fixture {
+  return createFixturePlugin({
+    id: CONSUMER_ID,
+    permissions: [TRANSPORT_OWNER_CAPABILITY],
+    backendSource: CONSUMER_SOURCE,
+    manifestOverrides: { category: "Infrastructure", requiresSecret },
+  });
+}
+
+function borrow(userId = "user-1"): Promise<string | null> {
+  const fn = (globalThis as Record<string, unknown>).__borrow as (
+    id: string,
+  ) => Promise<string | null>;
+  return fn(userId);
+}
+
+function borrowUndeclared(userId = "user-1"): Promise<string | null> {
+  const fn = (globalThis as Record<string, unknown>).__borrowUndeclared as (
+    id: string,
+  ) => Promise<string | null>;
+  return fn(userId);
+}
+
+describe("cross-plugin secret references", () => {
+  let provider: Fixture | null = null;
+  let consumer: Fixture | null = null;
+  let loader: InstanceType<typeof PluginLoader> | null = null;
+  let valueFile = "";
+
+  beforeEach(() => {
+    state.granted = new Set([PERMISSION]);
+    state.auditEntries = [];
+    clearSecretRegistry();
+    pluginEvents.clear();
+  });
+
+  afterEach(async () => {
+    await loader?.shutdown();
+    loader = null;
+    provider?.cleanup();
+    consumer?.cleanup();
+    provider = null;
+    consumer = null;
+    delete (globalThis as Record<string, unknown>).__borrow;
+    delete (globalThis as Record<string, unknown>).__borrowUndeclared;
+    clearSecretRegistry();
+    pluginEvents.clear();
+  });
+
+  async function activateProvider() {
+    provider = providerFixture();
+    valueFile = path.join(provider.root, "secret.txt");
+    fs.writeFileSync(valueFile, SECRET);
+    fs.writeFileSync(
+      path.join(provider.dir, "backend", "index.mjs"),
+      providerSource(valueFile),
+    );
+
+    loader ??= new PluginLoader();
+    const plugin = await loader.load(provider.dir);
+    await loader.activate(plugin.id);
+    return plugin;
+  }
+
+  async function activateConsumer(
+    requiresSecret?: Array<Record<string, unknown>>,
+  ) {
+    consumer = requiresSecret
+      ? consumerFixture(requiresSecret)
+      : consumerFixture();
+
+    loader ??= new PluginLoader();
+    const plugin = await loader.load(consumer.dir);
+    await loader.activate(plugin.id);
+    return plugin;
+  }
+
+  async function activateBoth() {
+    loader = new PluginLoader();
+    const providerPlugin = await activateProvider();
+    const consumerPlugin = await activateConsumer();
+    return { providerPlugin, consumerPlugin };
+  }
+
+  it("registers the offer when the provider activates", async () => {
+    const { providerPlugin, consumerPlugin } = await activateBoth();
+
+    expect(providerPlugin.state).toBe("active");
+    expect(consumerPlugin.state).toBe("active");
+
+    const registration = getSecretRegistration(PROVIDER_ID, KEY);
+    expect(registration?.pluginId).toBe(PROVIDER_ID);
+    expect(registration?.permission).toBe(PERMISSION);
+  });
+
+  it("resolves for a user who holds the permission", async () => {
+    await activateBoth();
+
+    await expect(borrow()).resolves.toBe(SECRET);
+  });
+
+  it("denies a user without the permission, though the secret is set", async () => {
+    await activateBoth();
+    state.granted = new Set();
+
+    await expect(borrow("user-2")).rejects.toBeInstanceOf(
+      PluginSecretPermissionError,
+    );
+    // Still installed, still set: the difference is purely this user's role.
+    expect(getSecretRegistration(PROVIDER_ID, KEY)).toBeDefined();
+    expect(fs.readFileSync(valueFile, "utf8")).toBe(SECRET);
+  });
+
+  it("lets one user borrow while another is denied, with no reinstall", async () => {
+    await activateBoth();
+
+    // The grant is per-user, so both answers come from the same live install.
+    await expect(borrow("allowed-user")).resolves.toBe(SECRET);
+
+    state.granted = new Set();
+    await expect(borrow("denied-user")).rejects.toBeInstanceOf(
+      PluginSecretPermissionError,
+    );
+
+    state.granted = new Set([PERMISSION]);
+    await expect(borrow("allowed-user")).resolves.toBe(SECRET);
+  });
+
+  it("returns null when the provider is installed but the key is not set", async () => {
+    await activateBoth();
+    fs.writeFileSync(valueFile, "");
+
+    await expect(borrow()).resolves.toBeNull();
+  });
+
+  it("returns null when the providing plugin was never installed", async () => {
+    loader = new PluginLoader();
+    await activateConsumer();
+
+    // The consumer activates regardless: the reference is resolved per call.
+    await expect(borrow()).resolves.toBeNull();
+  });
+
+  it("activates the consumer even when a non-optional reference is absent", async () => {
+    loader = new PluginLoader();
+    const plugin = await activateConsumer([{ plugin: PROVIDER_ID, key: KEY }]);
+
+    // Unlike a service requirement, an absent secret provider is recoverable
+    // by installing it later, so it must not be a hard ordering dependency.
+    expect(plugin.state).toBe("active");
+    await expect(borrow()).resolves.toBeNull();
+  });
+
+  it("refuses a read the consumer's manifest never declared", async () => {
+    await activateBoth();
+
+    await expect(borrowUndeclared()).rejects.toBeInstanceOf(
+      PluginSecretUndeclaredError,
+    );
+  });
+
+  it("refuses to offer a secret the provider's manifest never declared", async () => {
+    provider = createFixturePlugin({
+      id: PROVIDER_ID,
+      permissions: [TRANSPORT_OWNER_CAPABILITY],
+      backendSource: `
+export async function activate(ctx) {
+  ctx.secrets.offer("undeclared-key", () => "nope");
+}
+`,
+      manifestOverrides: {
+        category: "Terminal",
+        providesSecret: [{ key: KEY, permission: PERMISSION }],
+        contributes: {
+          permissionGroup: { group: "testplugin", permissions: [PERMISSION] },
+        },
+      },
+    });
+
+    loader = new PluginLoader();
+    const plugin = await loader.load(provider.dir);
+    await loader.activate(plugin.id).catch(() => undefined);
+
+    expect(plugin.state).not.toBe("active");
+    expect(
+      getSecretRegistration(PROVIDER_ID, "undeclared-key"),
+    ).toBeUndefined();
+  });
+
+  describe("the provider stays in control", () => {
+    it("serves a rotated value on the next borrow", async () => {
+      await activateBoth();
+      await expect(borrow()).resolves.toBe(SECRET);
+
+      fs.writeFileSync(valueFile, "sk-fixture-rotated");
+
+      // Nothing to invalidate: the borrower never held a copy to go stale.
+      await expect(borrow()).resolves.toBe("sk-fixture-rotated");
+    });
+
+    it("nulls the borrow out when the provider clears the secret", async () => {
+      await activateBoth();
+      await expect(borrow()).resolves.toBe(SECRET);
+
+      fs.rmSync(valueFile);
+
+      await expect(borrow()).resolves.toBeNull();
+    });
+  });
+
+  describe("uninstalling the provider", () => {
+    it("nulls out the reference rather than leaving a dangling handle", async () => {
+      const { providerPlugin } = await activateBoth();
+      await expect(borrow()).resolves.toBe(SECRET);
+
+      await loader!.deactivate(providerPlugin.id);
+
+      // The borrower is untouched: still active, still permitted, still
+      // declaring the reference. It just gets null now, and does not throw.
+      expect(getSecretRegistration(PROVIDER_ID, KEY)).toBeUndefined();
+      await expect(borrow()).resolves.toBeNull();
+    });
+
+    it("keeps serving nothing even though the underlying value still exists", async () => {
+      const { providerPlugin } = await activateBoth();
+      await loader!.deactivate(providerPlugin.id);
+
+      // The file is still on disk. Access went away with the plugin that
+      // mediated it, which is the point: there was never a copy to fall back on.
+      expect(fs.readFileSync(valueFile, "utf8")).toBe(SECRET);
+      await expect(borrow()).resolves.toBeNull();
+    });
+
+    it("resumes when the provider is reinstalled, with no borrower restart", async () => {
+      const { providerPlugin } = await activateBoth();
+      await loader!.deactivate(providerPlugin.id);
+      await expect(borrow()).resolves.toBeNull();
+
+      await loader!.activate(providerPlugin.id);
+
+      await expect(borrow()).resolves.toBe(SECRET);
+    });
+  });
+
+  describe("audit", () => {
+    it("records a borrow without the value", async () => {
+      await activateBoth();
+      await borrow("user-9");
+
+      const entry = state.auditEntries.at(-1);
+      expect(entry).toMatchObject({
+        userId: "user-9",
+        username: `plugin:${CONSUMER_ID}`,
+        action: "plugin_secret_shared_read",
+        resourceId: PROVIDER_ID,
+        success: true,
+      });
+      expect(JSON.stringify(state.auditEntries)).not.toContain(SECRET);
+    });
+
+    it("records a denial without the value", async () => {
+      await activateBoth();
+      state.granted = new Set();
+      await borrow().catch(() => undefined);
+
+      expect(state.auditEntries.at(-1)).toMatchObject({ success: false });
+      expect(JSON.stringify(state.auditEntries)).not.toContain(SECRET);
+    });
+  });
+});

src/backend/tests/plugins/secret-registry.test.ts

@@ -0,0 +1,424 @@
+/**
+ * Cross-plugin secret references: the permission gate, the two null cases, and
+ * what an uninstall does to a borrower still pointing at the provider.
+ *
+ * The distinction under test throughout is between a denial (an error, because
+ * the caller asked for something it may not have) and an absence (null, because
+ * the thing legitimately is not there). A consumer that cannot tell those apart
+ * would read "you may not" as "not configured" and fall back to something
+ * weaker, so every case below asserts which of the two it got.
+ */
+
+import { afterEach, beforeEach, describe, expect, it, vi } from "vitest";
+
+vi.mock("../../utils/logger.js", () => ({
+  pluginLogger: {
+    debug: vi.fn(),
+    info: vi.fn(),
+    warn: vi.fn(),
+    error: vi.fn(),
+    success: vi.fn(),
+  },
+}));
+
+const {
+  clearSecretRegistry,
+  getSecretRegistration,
+  listSecrets,
+  offerSecret,
+  readSharedSecret,
+  resolveSecretRequirements,
+  withdrawAllForPlugin,
+  withdrawSecret,
+  PluginSecretActorError,
+  PluginSecretPermissionError,
+  PluginSecretUndeclaredError,
+} = await import("../../plugins/secret-registry.js");
+
+const PROVIDER = "ai-assistant";
+const KEY = "api-key";
+const PERMISSION = "ai.secrets.share";
+const SECRET = "sk-live-value";
+
+/** Permissions the acting user currently holds. Mutated mid-test. */
+let granted = new Set<string>();
+let auditEntries: Array<Record<string, unknown>> = [];
+
+function offer(overrides: Partial<Parameters<typeof offerSecret>[0]> = {}) {
+  return offerSecret({
+    pluginId: PROVIDER,
+    pluginName: "AI Assistant",
+    key: KEY,
+    permission: PERMISSION,
+    resolve: () => SECRET,
+    ...overrides,
+  });
+}
+
+/** A consumer manifest declaring the reference, as the real one would. */
+function consumer(
+  requiresSecret: Array<{ plugin: string; key: string; optional?: boolean }> = [
+    { plugin: PROVIDER, key: KEY, optional: true },
+  ],
+) {
+  return { id: "reporting-plugin", requiresSecret } as never;
+}
+
+function context(userId: string | undefined) {
+  return {
+    resolveUserId: () => userId,
+    hasPermission: async (_userId: string, permission: string) =>
+      granted.has(permission),
+    audit: (entry: Record<string, unknown>) => {
+      auditEntries.push(entry);
+    },
+  } as never;
+}
+
+function read(
+  manifest = consumer(),
+  userId: string | undefined = "user-1",
+  providerPluginId = PROVIDER,
+  key = KEY,
+) {
+  return readSharedSecret(manifest, providerPluginId, key, context(userId));
+}
+
+/**
+ * A read with no acting user. Separate from read() on purpose: a default
+ * parameter cannot express this, since passing undefined explicitly would
+ * just fall back to the default and quietly test the wrong thing.
+ */
+function readAnonymously(manifest = consumer()) {
+  return readSharedSecret(manifest, PROVIDER, KEY, context(undefined));
+}
+
+describe("shared secret registry", () => {
+  beforeEach(() => {
+    clearSecretRegistry();
+    granted = new Set([PERMISSION]);
+    auditEntries = [];
+  });
+  afterEach(() => clearSecretRegistry());
+
+  describe("registration", () => {
+    it("round-trips an offer", () => {
+      const registration = offer();
+
+      expect(getSecretRegistration(PROVIDER, KEY)).toBe(registration);
+      expect(listSecrets()).toHaveLength(1);
+      expect(registration.generation).toBeGreaterThan(0);
+    });
+
+    it("keys offers by plugin as well as name", () => {
+      offer();
+      offer({ pluginId: "other-plugin", resolve: () => "other-value" });
+
+      expect(listSecrets()).toHaveLength(2);
+      expect(getSecretRegistration("other-plugin", KEY)?.pluginId).toBe(
+        "other-plugin",
+      );
+    });
+
+    it("only withdraws the offer that is actually current", () => {
+      const first = offer();
+      const second = offer();
+
+      // A crashed-and-restarted provider must not withdraw the replacement its
+      // own restart installed.
+      expect(withdrawSecret(PROVIDER, KEY, first)).toBe(false);
+      expect(getSecretRegistration(PROVIDER, KEY)).toBe(second);
+
+      expect(withdrawSecret(PROVIDER, KEY, second)).toBe(true);
+      expect(getSecretRegistration(PROVIDER, KEY)).toBeUndefined();
+    });
+
+    it("reports a withdraw of something never offered", () => {
+      expect(withdrawSecret(PROVIDER, "nothing")).toBe(false);
+    });
+  });
+
+  describe("reading", () => {
+    it("resolves for a user who holds the permission", async () => {
+      offer();
+
+      await expect(read()).resolves.toBe(SECRET);
+    });
+
+    it("denies a user without the permission, though the secret exists", async () => {
+      offer();
+      granted = new Set();
+
+      // The whole point of the per-call check: the plugin is installed, the
+      // key is set, and this user still gets nothing.
+      await expect(read()).rejects.toBeInstanceOf(PluginSecretPermissionError);
+      expect(getSecretRegistration(PROVIDER, KEY)).toBeDefined();
+    });
+
+    it("denies with the 403 shape a route can pass straight through", async () => {
+      offer();
+      granted = new Set();
+
+      const error = await read().catch((caught) => caught);
+
+      expect(error.status).toBe(403);
+      expect(error.body).toEqual({
+        error: "Insufficient permissions",
+        required: PERMISSION,
+      });
+    });
+
+    it("never runs the provider's resolver for a denied read", async () => {
+      const resolve = vi.fn(() => SECRET);
+      offer({ resolve });
+      granted = new Set();
+
+      await expect(read()).rejects.toBeInstanceOf(PluginSecretPermissionError);
+      expect(resolve).not.toHaveBeenCalled();
+    });
+
+    it("returns null when the provider is installed but the key is not set", async () => {
+      offer({ resolve: () => null });
+
+      // Absence, not denial: the user may read it, there is just nothing there.
+      await expect(read()).resolves.toBeNull();
+    });
+
+    it("treats an empty string as not set", async () => {
+      offer({ resolve: () => "" });
+
+      await expect(read()).resolves.toBeNull();
+    });
+
+    it("returns null when the providing plugin is not installed at all", async () => {
+      await expect(read()).resolves.toBeNull();
+    });
+
+    it("gives the same answer for absent and unset, so neither leaks install state", async () => {
+      const unset = await read();
+      offer({ resolve: () => null });
+      const absent = await read();
+
+      expect(unset).toBeNull();
+      expect(absent).toBeNull();
+    });
+
+    it("refuses a plugin reading something its manifest never declared", async () => {
+      offer();
+
+      await expect(read(consumer([]), "user-1")).rejects.toBeInstanceOf(
+        PluginSecretUndeclaredError,
+      );
+    });
+
+    it("refuses a declared reference to a different key on the same plugin", async () => {
+      offer();
+
+      await expect(
+        read(consumer([{ plugin: PROVIDER, key: "other-key" }])),
+      ).rejects.toBeInstanceOf(PluginSecretUndeclaredError);
+    });
+
+    it("refuses a read that cannot be attributed to a user", async () => {
+      offer();
+
+      await expect(readAnonymously()).rejects.toBeInstanceOf(
+        PluginSecretActorError,
+      );
+    });
+
+    it("returns null for an anonymous read of an absent provider", async () => {
+      // Absence is settled before the actor is, so a borrower whose provider
+      // is gone gets the same null whether or not it had a user to act as.
+      await expect(readAnonymously()).resolves.toBeNull();
+    });
+
+    it("passes the acting user to the resolver, so per-user keys stay per-user", async () => {
+      const resolve = vi.fn((userId: string) => `key-for-${userId}`);
+      offer({ resolve });
+
+      await expect(read(consumer(), "user-7")).resolves.toBe("key-for-user-7");
+      expect(resolve).toHaveBeenCalledWith("user-7");
+    });
+
+    it("propagates a resolver failure rather than reporting it as unset", async () => {
+      offer({
+        resolve: () => {
+          throw new Error("vault unreachable");
+        },
+      });
+
+      // Reported as null, a consumer would fall back to a weaker path on what
+      // is actually a transient provider fault.
+      await expect(read()).rejects.toThrow("vault unreachable");
+    });
+  });
+
+  describe("revocation takes effect immediately", () => {
+    it("stops resolving the moment the permission is revoked", async () => {
+      offer();
+      await expect(read()).resolves.toBe(SECRET);
+
+      granted = new Set();
+
+      // No restart, no reinstall: the next call is already denied.
+      await expect(read()).rejects.toBeInstanceOf(PluginSecretPermissionError);
+    });
+
+    it("serves the rotated value on the next read, with nothing to invalidate", async () => {
+      let current = SECRET;
+      offer({ resolve: () => current });
+
+      await expect(read()).resolves.toBe(SECRET);
+      current = "sk-live-rotated";
+      await expect(read()).resolves.toBe("sk-live-rotated");
+    });
+
+    it("nulls out a borrower's reference when the provider clears the secret", async () => {
+      let current: string | null = SECRET;
+      offer({ resolve: () => current });
+
+      await expect(read()).resolves.toBe(SECRET);
+      current = null;
+      await expect(read()).resolves.toBeNull();
+    });
+  });
+
+  describe("uninstalling the provider", () => {
+    it("nulls out the reference rather than leaving a dangling handle", async () => {
+      offer();
+      await expect(read()).resolves.toBe(SECRET);
+
+      expect(withdrawAllForPlugin(PROVIDER)).toBe(1);
+
+      // The borrower is still installed, still declares the reference, and
+      // still holds the permission. It simply gets null now, the same answer
+      // as a provider that was never installed -- no throw, no stale value.
+      await expect(read()).resolves.toBeNull();
+      expect(getSecretRegistration(PROVIDER, KEY)).toBeUndefined();
+    });
+
+    it("keeps no copy of the value behind after an uninstall", async () => {
+      const resolve = vi.fn(() => SECRET);
+      offer({ resolve });
+      await read();
+      resolve.mockClear();
+
+      withdrawAllForPlugin(PROVIDER);
+
+      // Nothing cached the earlier read: the answer comes from the absence of
+      // a registration, not from a remembered value.
+      await expect(read()).resolves.toBeNull();
+      expect(resolve).not.toHaveBeenCalled();
+    });
+
+    it("withdraws every key the plugin offered, not just the one read", () => {
+      offer();
+      offer({ key: "webhook-secret" });
+      offer({ pluginId: "unrelated-plugin" });
+
+      expect(withdrawAllForPlugin(PROVIDER)).toBe(2);
+      expect(listSecrets()).toHaveLength(1);
+      expect(getSecretRegistration("unrelated-plugin", KEY)).toBeDefined();
+    });
+
+    it("starts working again if the provider is reinstalled, with no borrower restart", async () => {
+      offer();
+      withdrawAllForPlugin(PROVIDER);
+      await expect(read()).resolves.toBeNull();
+
+      offer({ resolve: () => "sk-live-reinstalled" });
+
+      await expect(read()).resolves.toBe("sk-live-reinstalled");
+    });
+  });
+
+  describe("requirement resolution", () => {
+    it("reports an offered reference as available", () => {
+      offer();
+
+      const resolution = resolveSecretRequirements(consumer());
+
+      expect(resolution.available).toEqual([`${PROVIDER}:${KEY}`]);
+      expect(resolution.unavailable).toEqual([]);
+      expect(resolution.errors).toEqual([]);
+    });
+
+    it("reports an absent optional reference without an error", () => {
+      const resolution = resolveSecretRequirements(consumer());
+
+      expect(resolution.unavailable).toEqual([`${PROVIDER}:${KEY}`]);
+      expect(resolution.errors).toEqual([]);
+    });
+
+    it("reports an absent required reference as an error", () => {
+      const resolution = resolveSecretRequirements(
+        consumer([{ plugin: PROVIDER, key: KEY }]),
+      );
+
+      expect(resolution.errors).toHaveLength(1);
+      expect(resolution.errors[0]).toContain(PROVIDER);
+    });
+
+    it("ignores any user's permissions, because activation is per-instance", () => {
+      offer();
+      granted = new Set();
+
+      // A user without the grant must get a clear denial from the call, not a
+      // plugin that mysteriously refuses to start.
+      expect(resolveSecretRequirements(consumer()).available).toHaveLength(1);
+    });
+
+    it("is empty for a manifest that borrows nothing", () => {
+      const resolution = resolveSecretRequirements({ id: "plain" } as never);
+
+      expect(resolution.available).toEqual([]);
+      expect(resolution.unavailable).toEqual([]);
+      expect(resolution.errors).toEqual([]);
+    });
+  });
+
+  describe("audit", () => {
+    it("records an allowed read without the value", async () => {
+      offer();
+      await read();
+
+      expect(auditEntries).toHaveLength(1);
+      expect(auditEntries[0]).toMatchObject({
+        userId: "user-1",
+        consumerPluginId: "reporting-plugin",
+        providerPluginId: PROVIDER,
+        key: KEY,
+        success: true,
+        resolved: true,
+      });
+      expect(JSON.stringify(auditEntries[0])).not.toContain(SECRET);
+    });
+
+    it("records a denial", async () => {
+      offer();
+      granted = new Set();
+      await read().catch(() => undefined);
+
+      expect(auditEntries[0]).toMatchObject({
+        success: false,
+        resolved: false,
+      });
+    });
+
+    it("distinguishes an allowed read that found nothing", async () => {
+      offer({ resolve: () => null });
+      await read();
+
+      expect(auditEntries[0]).toMatchObject({ success: true, resolved: false });
+    });
+
+    it("writes nothing when the provider is not installed", async () => {
+      await read();
+
+      // There is no provider to attribute the read to, and no decision was
+      // made about the user -- an audit line here would be noise.
+      expect(auditEntries).toEqual([]);
+    });
+  });
+});

src/ui/locales/en.json

@@ -5049,7 +5049,10 @@
     "noProvidersConfigured": "No AI provider is configured yet. Add one in the AI assistant tab.",
     "runsInOpenTerminal": "Runs in your open terminal session.",
     "runInTerminal": "Run",
-    "terminalContextPrefill": "Here is my terminal output:\n\n{{output}}\n\n"
+    "terminalContextPrefill": "Here is my terminal output:\n\n{{output}}\n\n",
+    "secrets": {
+      "shareApiKey": "Let other plugins use your AI provider API key for their own requests. The key is never copied, and you can revoke this at any time."
+    }
   },
   "macros": {
     "title": "Macros",