refactor: brand the request id

[jakedipity]

RequestId becomes a newtype over String instead of a type alias, so a bare string can no longer stand in for a request id. It threads through SSE routing, the tool-event broker, MCP cancellation, HITL approval gates, the session store, and the scratchpad's per-request directory.

The brokers and the cancellation registry key their maps by RequestId rather than String. In mcp/client.rs, rmcp's own RequestId is imported as McpRequestId, so the HTTP request id and the MCP protocol request id are no longer the same type in signatures that take both.

The webhook payload and stored approval records keep their bare-string shape, which serde(transparent) guarantees and a record test now pins.

[greptile-apps]

Greptile Summary

The PR replaces bare request-ID strings with a dedicated RequestId newtype while preserving existing serialized record and webhook shapes.

• Threads the branded identifier through streaming, orchestration, HITL, MCP cancellation, brokers, session storage, and scratchpad paths.
• Keys request-scoped registries and brokers by RequestId.
• Aliases rmcp’s protocol identifier as McpRequestId where both identifier domains appear.
• Adds coverage pinning the persisted request ID to a bare JSON string.

Confidence Score: 5/5

The PR appears safe to merge.

No blocking failure remains.

Important Files Changed

Filename	Overview
crates/aura/src/config.rs	Defines the branded request identifier and its transparent string representation.
crates/aura/src/mcp/client.rs	Separates Aura request identifiers from rmcp protocol request identifiers in MCP operations.
crates/aura/src/request_cancellation.rs	Migrates cancellation-registry keys and APIs from strings to RequestId.
crates/aura/src/tool_event_broker.rs	Migrates request-scoped tool-event broker keys and calls to the branded identifier.
crates/aura/src/session_store/record.rs	Stores RequestId directly and pins its enduring bare-string JSON contract with a focused test.
crates/aura-web-server/src/streaming/handlers.rs	Threads the branded request identifier through the web server’s streaming request lifecycle.

Flowchart

%%{init: {'theme': 'neutral'}}%%
flowchart LR
    HTTP[HTTP / A2A request] --> RID[RequestId newtype]
    RID --> STREAM[Streaming and SSE routing]
    RID --> HITL[HITL approval gates]
    RID --> BROKERS[Progress and tool-event brokers]
    RID --> CANCEL[Request and MCP cancellation]
    RID --> STORE[Session and approval storage]
    RID --> SCRATCH[Per-request scratchpad]
    STORE -->|serde transparent| JSON[Bare-string persisted shape]

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_{Reviews (4): Last reviewed commit: "refactor: brand the request id" | Re-trigger Greptile}

[Shearerbeard]

My only feedback here is that lib.rs is to general - if were starting to consolidate code around building our domain types and events lets just call it domain

[Shearerbeard]

This looks good - as we progress we might have to better module classify identifiers a cross application concerns (like RequestId) vs agent specific new types like AgentId. There are probably a few cross cutting concerns to belong in a root domain vs a specific one. Also a good place to start looking for duplicated construction and validation code if it exists (I don't see that here - just the kind of thing I like to think ahead on when designing by types)

The base branch was changed.