> ## Documentation Index > Fetch the complete documentation index at: https://help.harmonica.chat/llms.txt > Use this file to discover all available pages before exploring further. # Request guarded host chain progression > Requires owner/admin access to the origin session. Platform session metadata audit keys cannot advance chains, even for a session they own. Pass current_step_id from chain-state as expected_step_id. No force, trigger override, credit-retry query option or completion bypass exists in this API-key contract. Existing empty-body browser UI/internal calls retain their legacy response contract and are not described here. Completion/quorum/timer and role readiness use the normal runtime rules. Missing predecessor summaries return summary_required blockers without enqueueing work or changing state; generate those summaries through the existing summary API/tool, then retry with the same expected step. Rejected preconditions make no chain writes. A runtime handoff failure retains the normal runtime pause behavior and returns advance_failed. A committed transition stores actor/transport evidence atomically. A retry of that expected step returns its original receipt with replayed=true, without creating sessions/assignments or redispatching notifications. The normal runtime may catch up additional already-complete automatic steps; inspect chain-state again for the latest frontier. Normal progression may reserve credits and email assigned roster participants. ## OpenAPI ````yaml /api-reference/openapi.yaml post /sessions/{id}/continue-chain openapi: 3.1.0 info: title: Harmonica API version: 1.0.0 description: > REST API for the Harmonica structured deliberation platform. Provides access to sessions and their data, including creating, updating, and querying sessions, plus response submission for active sessions. contact: name: Harmonica url: https://harmonica.chat servers: - url: https://app.harmonica.chat/api/v1 description: Production - url: http://localhost:3000/api/v1 description: Local development security: - apiKey: [] paths: /sessions/{id}/continue-chain: post: tags: - Sessions summary: Request guarded host chain progression description: > Requires owner/admin access to the origin session. Platform session metadata audit keys cannot advance chains, even for a session they own. Pass current_step_id from chain-state as expected_step_id. No force, trigger override, credit-retry query option or completion bypass exists in this API-key contract. Existing empty-body browser UI/internal calls retain their legacy response contract and are not described here. Completion/quorum/timer and role readiness use the normal runtime rules. Missing predecessor summaries return summary_required blockers without enqueueing work or changing state; generate those summaries through the existing summary API/tool, then retry with the same expected step. Rejected preconditions make no chain writes. A runtime handoff failure retains the normal runtime pause behavior and returns advance_failed. A committed transition stores actor/transport evidence atomically. A retry of that expected step returns its original receipt with replayed=true, without creating sessions/assignments or redispatching notifications. The normal runtime may catch up additional already-complete automatic steps; inspect chain-state again for the latest frontier. Normal progression may reserve credits and email assigned roster participants. operationId: continueChain parameters: - name: id in: path required: true schema: type: string requestBody: required: true content: application/json: schema: type: object additionalProperties: false required: - expected_step_id properties: expected_step_id: type: string minLength: 1 maxLength: 200 responses: '200': description: Original or replayed committed transition receipt content: application/json: schema: $ref: '#/components/schemas/ChainHostAdvanceReceipt' '400': description: Invalid request body or unsupported query override '401': description: Authentication required '403': description: Origin owner/admin required or metadata audit key refused '404': description: Session is not part of a chain or chain not found '409': description: Stale step or unmet prerequisites or failed runtime handoff content: application/json: schema: $ref: '#/components/schemas/ChainControlError' '500': description: Internal error components: schemas: ChainHostAdvanceReceipt: type: object required: - chain_id - from_step_id - action - next_step_id - next_session_id - actor_id - auth_method - source - occurred_at - replayed properties: chain_id: type: string from_step_id: type: string action: type: string enum: - advanced - closed next_step_id: type: - string - 'null' next_session_id: type: - string - 'null' actor_id: type: string auth_method: type: string enum: - session - api_key source: type: string enum: - api - mcp description: >- Original committing transport; replay preserves the original actor and source. occurred_at: type: string format: date-time replayed: type: boolean ChainControlError: type: object required: - error properties: error: type: object required: - code - message properties: code: type: string enum: - forbidden - not_found - invalid_request - validation_error - stale_step - transition_blocked - advance_failed - internal_error message: type: string blockers: type: array items: $ref: '#/components/schemas/ChainBlocker' ChainBlocker: type: object required: - code - message properties: code: type: string enum: - chain_not_active - step_not_active - invalid_snapshot - unassigned_roles - completion_not_met - summary_required message: type: string step_id: type: string session_id: type: - string - 'null' securitySchemes: apiKey: type: http scheme: bearer description: | API key authentication. Pass your key as a Bearer token. Keys use the format `hm_live_<32 hex chars>`. Generate keys from your Harmonica dashboard settings. ```` This documentation is built and hosted on [Mintlify](https://mintlify.com), a developer documentation platform.