diff --git a/openspec/changes/fix-doctor-json-schema-cargo-installer/.openspec.yaml b/openspec/changes/fix-doctor-json-schema-cargo-installer/.openspec.yaml
new file mode 100644
index 0000000..ac20efa
--- /dev/null
+++ b/openspec/changes/fix-doctor-json-schema-cargo-installer/.openspec.yaml
@@ -0,0 +1,2 @@
+schema: spec-driven
+created: 2026-05-10
diff --git a/openspec/changes/fix-doctor-json-schema-cargo-installer/proposal.md b/openspec/changes/fix-doctor-json-schema-cargo-installer/proposal.md
new file mode 100644
index 0000000..4af571f
--- /dev/null
+++ b/openspec/changes/fix-doctor-json-schema-cargo-installer/proposal.md
@@ -0,0 +1,13 @@
+## Why
+
+Cargo support added a `cargo` boolean to `quantex doctor --json` under `data.installers`, but the doctor entry in `quantex schema doctor` still described only `brew`, `bun`, `npm`, and `winget`. With `additionalProperties: false`, any consumer validating doctor output against the published schema incorrectly rejects valid payloads.
+
+## What Changes
+
+- Extend the doctor `dataSchema.installers` contract to include `cargo` alongside the other managed installer flags.
+- Lock the alignment in tests and sync the agent-update spec narrative used for diagnostics contracts.
+
+## Impact
+
+- Affected specs: `openspec/specs/agent-update/spec.md`.
+- Affected code: `src/commands/schema.ts`, `test/commands/schema.test.ts`.
diff --git a/openspec/changes/fix-doctor-json-schema-cargo-installer/specs/agent-update/spec.md b/openspec/changes/fix-doctor-json-schema-cargo-installer/specs/agent-update/spec.md
new file mode 100644
index 0000000..d1a6ae0
--- /dev/null
+++ b/openspec/changes/fix-doctor-json-schema-cargo-installer/specs/agent-update/spec.md
@@ -0,0 +1,12 @@
+## ADDED Requirements
+
+### Requirement: Doctor JSON schema MUST stay aligned with doctor installer diagnostics
+
+The machine-readable schema for `quantex doctor` SHALL enumerate every installer availability flag that structured doctor output can emit, so validators using `additionalProperties: false` accept real doctor JSON.
+
+#### Scenario: Doctor schema includes Cargo alongside other managed installers
+
+- **GIVEN** the user runs `quantex schema doctor` in JSON mode
+- **WHEN** Quantex returns the doctor command `dataSchema`
+- **THEN** `dataSchema.properties.installers.properties` includes a `cargo` boolean field
+- **AND** `dataSchema.properties.installers.required` includes `cargo` together with the other managed installer keys
diff --git a/openspec/changes/fix-doctor-json-schema-cargo-installer/tasks.md b/openspec/changes/fix-doctor-json-schema-cargo-installer/tasks.md
new file mode 100644
index 0000000..d02d075
--- /dev/null
+++ b/openspec/changes/fix-doctor-json-schema-cargo-installer/tasks.md
@@ -0,0 +1,3 @@
+- [x] 1.1 Add `cargo` to doctor JSON schema `installers` properties and `required` list in `src/commands/schema.ts`.
+- [x] 1.2 Assert schema parity in `test/commands/schema.test.ts`.
+- [x] 1.3 Document the contract in `openspec/specs/agent-update/spec.md`.
diff --git a/openspec/specs/agent-update/spec.md b/openspec/specs/agent-update/spec.md
index ce2bbd0..868a403 100644
--- a/openspec/specs/agent-update/spec.md
+++ b/openspec/specs/agent-update/spec.md
@@ -150,6 +150,13 @@ Agent update behavior SHALL be inspectable through user-facing diagnostic comman
 - AND includes `subject`, `suggestedAction`, and `suggestedCommands`
 - AND allows an automation layer to distinguish between inspection, self-update, and manual-follow-up paths
 
+#### Scenario: Doctor schema documents every managed installer availability flag
+
+- GIVEN the user runs `quantex schema doctor` in JSON mode
+- WHEN Quantex returns the doctor command `dataSchema`
+- THEN the `installers` object lists every managed installer key that `quantex doctor --json` may emit, including `cargo`
+- AND strict schema validation of real doctor JSON output does not fail solely because an installer flag is missing from the published schema
+
 #### Scenario: Resolve exposes machine-actionable install guidance
 
 - GIVEN the user runs `quantex resolve <agent> --json`
diff --git a/src/commands/schema.ts b/src/commands/schema.ts
index cfd7a83..cc19495 100644
--- a/src/commands/schema.ts
+++ b/src/commands/schema.ts
@@ -230,10 +230,11 @@ const schemaCatalog: SchemaDocument[] = [
           properties: {
             brew: { type: 'boolean' },
             bun: { type: 'boolean' },
+            cargo: { type: 'boolean' },
             npm: { type: 'boolean' },
             winget: { type: 'boolean' },
           },
-          required: ['brew', 'bun', 'npm', 'winget'],
+          required: ['brew', 'bun', 'cargo', 'npm', 'winget'],
           type: 'object',
         },
         issues: {
diff --git a/src/self/index.ts b/src/self/index.ts
index c0fc04a..29de90f 100644
--- a/src/self/index.ts
+++ b/src/self/index.ts
@@ -1,20 +1,5 @@
-import type {
-  SelfInspection,
-  SelfInstallSource,
-  SelfPackageMetadata,
-  SelfUpdateChannel,
-  SelfUpdateResult,
-  SelfUpgradePlan,
-} from './types'
+import type { SelfInspection, SelfInstallSource, SelfUpdateChannel, SelfUpdateResult, SelfUpgradePlan } from './types'
 import process from 'node:process'
-import {
-  canAutoUpdateSelf,
-  detectSelfInstallSource,
-  getSelfVersion,
-  reconcileSelfInstallSource,
-  resolveSelfInstallFacts,
-  resolveSelfPackageMetadata,
-} from './facts'
 import { acquireSelfUpgradeLock } from './lock'
 import {
   buildPlanFromInspection,
diff --git a/test/commands/schema.test.ts b/test/commands/schema.test.ts
index 8417ac9..2ae2e62 100644
--- a/test/commands/schema.test.ts
+++ b/test/commands/schema.test.ts
@@ -66,6 +66,8 @@ describe('schemaCommand', () => {
     expect(payload.data.commands[0].name).toBe('doctor')
     expect(payload.data.commands[0].dataSchema.properties.issues.items.properties.suggestedAction).toBeDefined()
     expect(payload.data.commands[0].dataSchema.properties.issues.items.properties.suggestedCommands).toBeDefined()
+    expect(payload.data.commands[0].dataSchema.properties.installers.properties.cargo).toEqual({ type: 'boolean' })
+    expect(payload.data.commands[0].dataSchema.properties.installers.required).toContain('cargo')
   })
 
   it('returns the exec schema in json mode', async () => {