Add repo-specific worktree artifact cleanup profiles

[chubes4]

Problem

Some repos are much more expensive per worktree than others. In the 2026-04-29 incident, homeboy@* worktrees were typically 2.5 GiB to 3.2 GiB each because Rust build artifacts live under target/. A few were larger than 6 GiB or 8 GiB.

Deleting old worktrees is the best cleanup, but DMC should also understand repo-specific build artifact profiles so it can explain and optionally reclaim large non-source directories safely.

Proposed solution

Add repo cleanup profiles to DMC workspace hygiene.

Examples:

• Rust/Homeboy: target/, possibly benchmark output dirs.
• Node repos: node_modules/, .next/, dist/, build caches when safe.
• WordPress/PHP repos: vendor/ only if composer can restore it and the worktree is not active.

The MVP can be conservative: report artifact sizes first, then add opt-in cleanup actions.

CLI behavior

Examples:

wp datamachine-code workspace worktree artifacts --format=json
wp datamachine-code workspace worktree cleanup --dry-run --include-artifacts
wp datamachine-code workspace worktree cleanup-artifacts --repo=homeboy --older-than=7d

Safety requirements

• Do not delete source files.
• Do not delete artifacts in dirty worktrees unless explicitly requested.
• Do not touch active Studio plugin/theme symlink targets.
• Artifact cleanup should be separate from worktree removal in output and stats.

Acceptance criteria

• DMC can report artifact size by worktree and by repo.
• Rust target/ directories are detected and summarized.
• Human output explains that removing the whole clean worktree is usually better than artifact-only cleanup.
• Any artifact deletion is opt-in and dry-run-able.

[chubes4]

Status update after workspace cleanup triage:

This issue is partially shipped, but not fully obsolete.

Already shipped:

• Cleanup/list output reports worktree size and artifact size.
• Rust target/ artifact detection is covered by smokes.
• Cleanup summaries expose artifact_size_bytes, artifact_size_by_repo, and top-size reporting.
• Human cleanup tables include artifact-size columns.

Remaining scope, if we keep this issue open:

• Decide whether artifact deletion is worth adding at all, versus recommending whole-worktree removal for clean merged worktrees.
• If yes, keep it separate from worktree deletion, e.g. cleanup-artifacts or --include-artifacts with dry-run/apply-plan semantics.
• Add repo-specific profiles only for safe, reconstructable artifacts (target/, node_modules/, build caches), never source files.
• Protect dirty/unpushed and active symlink-target worktrees unless explicitly overridden.

So the issue should now be read as “artifact cleanup action/profile follow-up,” not “artifact reporting.” Reporting is already done.