Align design-doc §13.2 with the backend probe/resolve seam

[leynos]

Summary

Follow-up to the merged #224 backend seam refactor. CodeRabbit's post-merge "Developer Documentation" warning flagged that docs/cuprum-design.md still described get_stream_backend() as delegating to _check_rust_available(), conflicting with the implemented probe→resolve seam.

The stale wording is in §13.2 (the "Extension Architecture" overview): it said the cached _check_rust_available() resolver wraps the probe "for is_rust_available() and get_stream_backend()", implying a direct delegation. §13.3 and §13.4 already describe the authoritative seam model (_parse_backend_value → _probe_rust_availability → _resolve_backend, with only _probe_rust_availability() wrapping the cached _check_rust_available()).

Change

Qualify the §13.2 sentence so get_stream_backend() is fed through the _probe_rust_availability() seam, mirroring §13.3, and add a one-line cross-reference to §13.4's full resolution plus an explicit "does not delegate to _check_rust_available() directly". The document now keeps one authoritative backend model; the high-level flowchart (which never claimed direct delegation) is unchanged.

Docs-only.

Validation

make markdownlint (49 files, 0 errors; spelling sub-target clean) and make nixie (all Mermaid diagrams validated) pass.

Summary by Sourcery

Documentation:

• Update §13.2 of the Cuprum design document to describe that get_stream_backend() uses the _probe_rust_availability() seam and clarify it does not delegate directly to _check_rust_available(), adding a cross-reference to §13.4’s full resolution flow.

[sourcery-ai]

Reviewer's guide (collapsed on small PRs)

Reviewer's Guide

Documentation-only update aligning the design doc’s description of the backend probe/resolve seam with the actual implementation, clarifying how get_stream_backend() uses the _probe_rust_availability() seam rather than delegating directly to _check_rust_available().

Sequence diagram for the updated backend probe/resolve seam used by get_stream_backend

sequenceDiagram
    participant Client
    participant get_stream_backend
    participant _parse_backend_value
    participant _probe_rust_availability
    participant _check_rust_available
    participant _resolve_backend

    Client->>get_stream_backend: get_stream_backend()
    get_stream_backend->>_parse_backend_value: _parse_backend_value(config_backend)
    _parse_backend_value-->>get_stream_backend: backend_value

    get_stream_backend->>_probe_rust_availability: _probe_rust_availability(backend_value)
    _probe_rust_availability->>_check_rust_available: _check_rust_available()
    _check_rust_available-->>_probe_rust_availability: rust_available
    _probe_rust_availability-->>get_stream_backend: probed_backend

    get_stream_backend->>_resolve_backend: _resolve_backend(probed_backend)
    _resolve_backend-->>get_stream_backend: backend_impl
    get_stream_backend-->>Client: backend_impl

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File-Level Changes

Change	Details	Files
Align §13.2 backend extension-architecture description with the implemented probe→resolve seam.	Clarify that get_stream_backend() is routed through the _probe_rust_availability() seam instead of directly delegating to _check_rust_available(). Add cross-reference to §13.4’s authoritative _parse_backend_value → _probe_rust_availability → _resolve_backend flow. Explicitly state that get_stream_backend() does not call _check_rust_available() directly, removing ambiguity with other sections.	docs/cuprum-design.md

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📥 Commits

Reviewing files that changed from the base of the PR and between 302858c and bc8e0a5.

📒 Files selected for processing (1)

• docs/cuprum-design.md

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