Rust extract_container_name treats empty segment as a container name (DELETE /containers/ is forwarded) #48

Problem

The three implementations disagree on DELETE /containers/ (empty segment in the container-name position) — same family as #24, opposite direction:

• Go (go/internal/proxy/router.go, extractContainerName): returns "", which is falsy → request falls through to default-deny (403).
• TypeScript (ts/src/proxy.ts, extractContainerName): returns undefined → default-deny (403).
• Rust (rs/src/proxy.rs, extract_container_name): returns Some("") → the lifecycle DELETE branch treats the empty string as a container name → unknown-container passthrough → Allow, and the request is forwarded to the Docker daemon.

Found during the merge-gate review of #43 (which fixed the Go side of #24; this divergence is pre-existing and not introduced there).

Impact

Low severity, same reasoning as #24: the daemon answers 404 for an empty name, so this is not exploitable on its own. But it is a real behavioural divergence between the "equal peer" implementations, and a request Go and TypeScript refuse to forward reaches the daemon when the deployment runs the Rust proxy.

Proposed solution

rs/src/proxy.rs::extract_container_name should return None for an empty name segment, matching Go/TS. Add the same test case in all three languages (DELETE /containers/ → 403) plus an integration check, so the row is pinned the way #43 pinned the reserved segments.

Alternatives considered

• Making Go/TS forward like Rust: rejected — default-deny is the repo's standing posture; forwarding a malformed path is the bug, not the deny.
• Folding the fix into fix(proxy): exclude reserved path segments from Go container name extraction #43: rejected — fix(proxy): exclude reserved path segments from Go container name extraction #43 is review-approved and scoped to the reserved-segment set; widening it re-opens the review.

Which implementation(s) would this affect?

• Go
• Rust
• TypeScript

Go and TypeScript get regression tests only; behaviour changes in Rust alone (convergence to the majority/deny behaviour, consistent with the equal-peers rule).