> ## Documentation Index > Fetch the complete documentation index at: https://checkfu.mintlify.site/llms.txt > Use this file to discover all available pages before exploring further. # Diff a forked Session against its source > Compares a fork with its recorded source: `id` must be a fork, and lineage is read from the branch's own ledger rather than from anything the caller claims. Returns the fork boundary (`through_event`, `through_sequence`), a tail summary per side past that boundary (positions scanned, event counts by type, the settling event, `last_seq`, and a `complete` flag that goes false when the bounded scan truncated), the diverged projection fields and both statuses, plus each side's Outcome and context-token totals. Unavailable positions are counted rather than guessed at, so erasure stays as visible here as in an export, and the whole view is derived on every read. An admin or root key may add `wire=true` for the model-wire drift block. Checkfu support posture: alpha; hosted. Required evidence journey: session-turn. Deployment-specific readiness and the latest proven release are available from GET /v1/support/capabilities. ## OpenAPI ````yaml /openapi.json get /v1/sessions/{id}/diff openapi: 3.1.0 info: title: Checkfu API version: '2026-08-27' description: >- Authentication is declared per operation: API-key, runtime, or connector bearer; Automation signature; or credential-free pairing redemption. Every general Checkfu REST request requires the dated `Checkfu-Version` header (one of: 2026-08-27); the three MCP JSON-RPC transports use `MCP-Protocol-Version`, A2A uses `A2A-Version`, and the provider OAuth callback carries neither Checkfu header. API keys resolve one Workspace without a request selector; authenticated responses identify it with `Checkfu-Workspace-Id`. servers: - url: https://api.checkfu.com security: - bearerAuth: [] tags: - name: organizations - name: sourceRepositories - name: tenants - name: workspaces - name: principals - name: principalGroups - name: principalAccessCredentials - name: apiKeys - name: agents - name: harnesses - name: harnessRuntime - name: sandboxProfiles - name: computerProfiles - name: permissionAssignments - name: actionPolicies - name: files - name: memoryStores - name: dreams - name: modelCredentials - name: modelRoutingProfiles - name: blueprintInstallations - name: toolSources - name: skills - name: skillSources - name: agentSources - name: skillProposals - name: instructionProposals - name: catalog - name: concepts - name: support - name: connections - name: connectionVaults - name: connectionAssignments - name: connectedRuntimes - name: projects - name: collaboration - name: automationGraphs - name: automations - name: actionApprovals - name: standingApprovals - name: usage - name: models - name: outcomes - name: budgets - name: billing - name: sessions - name: audit - name: sessionExports - name: runs - name: runnerPools - name: transcripts - name: sessionWatches - name: webhookEndpoints - name: integrationGateway - name: agentDeployments - name: workEnvironments - name: computers - name: computerScreens - name: computerBrowserObservations - name: computerBrowserActions - name: environments - name: vaults - name: apiMcp - name: a2a paths: /v1/sessions/{id}/diff: get: tags: - sessions summary: Diff a forked Session against its source description: >- Compares a fork with its recorded source: `id` must be a fork, and lineage is read from the branch's own ledger rather than from anything the caller claims. Returns the fork boundary (`through_event`, `through_sequence`), a tail summary per side past that boundary (positions scanned, event counts by type, the settling event, `last_seq`, and a `complete` flag that goes false when the bounded scan truncated), the diverged projection fields and both statuses, plus each side's Outcome and context-token totals. Unavailable positions are counted rather than guessed at, so erasure stays as visible here as in an export, and the whole view is derived on every read. An admin or root key may add `wire=true` for the model-wire drift block. Checkfu support posture: alpha; hosted. Required evidence journey: session-turn. Deployment-specific readiness and the latest proven release are available from GET /v1/support/capabilities. operationId: sessions.diffSession parameters: - name: id in: path schema: $ref: '#/components/schemas/SessionId' required: true - name: checkfu-version in: header schema: type: string enum: - '2026-08-27' required: true - name: wire in: query schema: type: string enum: - 'true' required: false responses: '200': description: Success content: application/json: schema: type: object properties: source: $ref: '#/components/schemas/SessionId' branch: $ref: '#/components/schemas/SessionId' through_event: $ref: '#/components/schemas/EventId' through_sequence: type: integer allOf: - exclusiveMinimum: 0 source_tail: $ref: '#/components/schemas/Objects_164' branch_tail: $ref: '#/components/schemas/Objects_164' projection: type: object properties: source_status: type: string branch_status: type: string diverged_fields: type: array items: type: string required: - source_status - branch_status - diverged_fields additionalProperties: false source_outcome: anyOf: - $ref: '#/components/schemas/Objects_165' - type: 'null' branch_outcome: anyOf: - $ref: '#/components/schemas/Objects_165' - type: 'null' source_context: anyOf: - $ref: '#/components/schemas/Objects_166' - type: 'null' branch_context: anyOf: - $ref: '#/components/schemas/Objects_166' - type: 'null' wire: type: object properties: canonical_form_version: type: number enum: - 1 source_calls: type: integer allOf: - minimum: 0 branch_calls: type: integer allOf: - minimum: 0 compared: type: integer allOf: - minimum: 0 matched: type: integer allOf: - minimum: 0 unreadable: type: integer allOf: - minimum: 0 truncated: type: boolean first_divergence: anyOf: - type: object properties: index: type: integer allOf: - minimum: 0 source_seq: anyOf: - type: integer - type: 'null' branch_seq: anyOf: - type: integer - type: 'null' required: - index - source_seq - branch_seq additionalProperties: false - type: 'null' required: - canonical_form_version - source_calls - branch_calls - compared - matched - unreadable - truncated - first_divergence additionalProperties: false required: - source - branch - through_event - through_sequence - source_tail - branch_tail - projection - source_outcome - branch_outcome - source_context - branch_context additionalProperties: false headers: checkfu-workspace-id: description: The Workspace resolved from the authenticated bearer credential. required: true schema: $ref: '#/components/schemas/WorkspaceId' '400': description: Typed Checkfu wire error content: application/json: schema: $ref: '#/components/schemas/ValidationMalformedError' '401': description: Typed Checkfu wire error content: application/json: schema: type: object required: - error properties: error: type: object required: - type - message - more properties: type: type: string enum: - auth.invalid_key message: type: string more: type: string enum: - >- https://docs.checkfu.com/reference/errors#auth-invalid-key description: >- Stable public documentation and remedy for this error type. additionalProperties: false additionalProperties: false '403': description: >- The organization, tenant, or workspace backing this key is administratively disabled. | Deployment governance or retention policy denied the request. content: application/json: schema: anyOf: - type: object required: - error properties: error: type: object properties: type: type: string enum: - auth.disabled_tenancy message: type: string more: type: string enum: - >- https://docs.checkfu.com/reference/errors#auth-disabled-tenancy description: >- Stable public documentation and remedy for this error type. required: - type - message - more additionalProperties: false additionalProperties: false - $ref: '#/components/schemas/PolicyDeniedError' '404': description: >- The requested resource does not exist in the resolved deployment boundary. content: application/json: schema: $ref: '#/components/schemas/ValidationNotFoundError' '429': description: Typed Checkfu wire error headers: retry-after: description: >- Delay in seconds for rate limits or deployment quotas with a known release or UTC reset boundary required: false schema: type: integer minimum: 1 content: application/json: schema: type: object required: - error properties: error: type: object required: - type - message - more properties: type: type: string enum: - budget.exceeded message: type: string more: type: string enum: - >- https://docs.checkfu.com/reference/errors#budget-exceeded description: >- Stable public documentation and remedy for this error type. additionalProperties: false additionalProperties: false '500': description: >- An unexpected internal failure occurred; the message contains an opaque incident reference. content: application/json: schema: $ref: '#/components/schemas/RuntimeInternalError' security: - bearerAuth: [] components: schemas: SessionId: type: string allOf: - pattern: ^sess_[0-9a-f]{32}$ EventId: type: string allOf: - pattern: ^evt_[0-9a-f]{32}$ Objects_164: type: object properties: session: $ref: '#/components/schemas/SessionId' positions: type: integer allOf: - minimum: 0 events: type: integer allOf: - minimum: 0 unavailable: type: integer allOf: - minimum: 0 by_type: type: array items: type: object properties: type: type: string count: type: integer allOf: - exclusiveMinimum: 0 required: - type - count additionalProperties: false settled: anyOf: - type: object properties: type: type: string seq: type: integer allOf: - exclusiveMinimum: 0 required: - type - seq additionalProperties: false - type: 'null' last_seq: type: integer allOf: - minimum: 0 complete: type: boolean required: - session - positions - events - unavailable - by_type - settled - last_seq - complete additionalProperties: false Objects_165: type: object properties: outcome: $ref: '#/components/schemas/OutcomeId' iteration: type: integer allOf: - minimum: 0 result: anyOf: - type: string - type: 'null' required: - outcome - iteration - result additionalProperties: false Objects_166: type: object properties: cumulative_tokens: type: integer allOf: - minimum: 0 current_context_tokens: type: integer allOf: - minimum: 0 condensations: type: integer allOf: - minimum: 0 required: - cumulative_tokens - current_context_tokens - condensations additionalProperties: false WorkspaceId: type: string allOf: - pattern: ^wrkspc_[0-9a-f]{32}$ ValidationMalformedError: type: object properties: error: type: object properties: type: type: string enum: - validation.malformed message: type: string more: type: string enum: - https://docs.checkfu.com/reference/errors#validation-malformed description: Stable public documentation and remedy for this error type. required: - type - message - more additionalProperties: false required: - error additionalProperties: false description: >- The request could not be decoded or violated a declared input constraint. PolicyDeniedError: type: object properties: error: type: object properties: type: type: string enum: - policy.denied message: type: string more: type: string enum: - https://docs.checkfu.com/reference/errors#policy-denied description: Stable public documentation and remedy for this error type. required: - type - message - more additionalProperties: false required: - error additionalProperties: false description: Deployment governance or retention policy denied the request. ValidationNotFoundError: type: object properties: error: type: object properties: type: type: string enum: - validation.not_found message: type: string more: type: string enum: - https://docs.checkfu.com/reference/errors#validation-not-found description: Stable public documentation and remedy for this error type. required: - type - message - more additionalProperties: false required: - error additionalProperties: false description: >- The requested resource does not exist in the resolved deployment boundary. RuntimeInternalError: type: object properties: error: type: object properties: type: type: string enum: - runtime.internal message: type: string more: type: string enum: - https://docs.checkfu.com/reference/errors#runtime-internal description: Stable public documentation and remedy for this error type. required: - type - message - more additionalProperties: false required: - error additionalProperties: false description: >- An unexpected internal failure occurred; the message contains an opaque incident reference. OutcomeId: type: string allOf: - pattern: ^outc_[0-9a-f]{32}$ securitySchemes: bearerAuth: type: http scheme: bearer ````