Drop the unused assert_cmd dev-dependency

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Question

Remove the unused assert_cmd dev-dependency, as decided in "portable-pty and assert_cmd: drop or build the pty harness": drop it from rust/dl/Cargo.toml:58 and the workspace list (rust/Cargo.toml:47); portable-pty stays (live in rust/aid/tests/interactive.rs). No behavior, so no red test — the proof is the pruned Cargo.lock and a clean cargo test --workspace.

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breadcrumb: entering building — wf-tdd stage subagent launched (manager: wf-mid run working map #299).

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breadcrumb: building. Restating the contract: remove the unused assert_cmd dev-dependency from the dl crate and the workspace dependency list; portable-pty stays. No behavior changes hands, so the ticket's stated exemption applies — no red test; the proof is the pruned Cargo.lock plus a green cargo test --workspace. Confirmed nothing in the tree imports assert_cmd before removing it.

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breadcrumb: built — PR #342 opened. One slice: assert_cmd removed from the workspace list and dl's dev-dependencies, Cargo.lock pruned of it and its five unique transitive crates; full workspace suite, clippy --locked, and fmt all green locally. portable-pty untouched.

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breadcrumb: build → in review. PR #342 pushed; all checks green (ci, rust, rust-coverage, e2e, public-api, packaging, prek, gate). Handing to a fresh wf-review context.

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breadcrumb: in review → reviewed. Two-axis review posted on #342 — Standards: pass, Spec: pass, verdict Approve (posted as a comment review; GitHub refuses self-approval). No blocking findings; three non-blocking notes (PR description miscounts the prune as five crates when it is six — difflib also goes; no cargo-udeps/machete guard in CI, which belongs to map #300; and a pre-existing unused dl entry in [workspace.dependencies]). Independently verified on the PR head: cargo metadata --locked --offline and cargo check --locked --all-targets both clean. Not merged — that stays human.

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breadcrumb: in review → approved, awaiting human merge. Two-axis report posted on PR #342: Standards pass, Spec pass, no blocking findings. The reviewer independently verified cargo metadata --locked --offline and cargo check --locked --all-targets on the PR head rather than trusting the PR body.

Three non-blocking notes it raised: the PR description miscounts the lockfile prune as five crates when it is six (difflib also goes, as predicates' only remaining dependent — the lockfile itself is correct); CI has no cargo-udeps/cargo-machete, which is how an unused dep survived at all, and that belongs on sibling map Drift-proofing rapid development rather than here; and rust/Cargo.toml:23 carries a pre-existing unused dl = { path = "dl" } in [workspace.dependencies], same class, out of this ticket's scope.

This ticket stays open until the PR is merged — the unattended lifecycle ends at approved.