refactor(perf): canonicalize the benchmark / wt-perf system

[max-sixty]

Implements the design proposal from this branch's first commit (b22aced, design/simplify-bench-perf.md — reviewable there; dropped from the merge candidate per the design/ convention). The perf tooling's emission side was already canonical; this consolidates the consumption side around one split: capture/harness work in wt-perf, analysis in worktrunk::trace with wt config state logs profile as its one CLI surface.

The seven design items:

1. wt-perf cache-check deleted — its output was the cache field of logs profile --format=json. The tend statusline recipe now uses logs profile (its old pipe also fed human-format stderr into a JSON parser, so it's now correct as well as canonical).
2. Timeline renderer moved into worktrunk::trace (src/trace/timeline.rs), sharing command_label/render_table/fmt_dur with the profile so the two views can't drift (they already had); drops wt-perf's tabwriter and insta deps. Durations now render in the profile's fixed-point format.
3. Profile.by_context (BY CONTEXT table + JSON array): per-worktree subprocess totals, the one analysis that previously required trace_processor SQL. The SQL sections in benches/CLAUDE.md and the trace module docs are replaced by a logs profile pointer; Perfetto stays for visual critical-path work.
4. One warm/cold bench runner (wt_perf::bench_wt) owns the BatchSize::PerIteration rationale once, replacing five inline copies. All runs now assert child exit status (benches/list.rs previously ignored it).
5. Bench matrix pruned: real_repo keeps only the 8-worktree variants (scaling shape stays on synthetic worktree_scaling), cow_copy deleted (benchmarked a hand-written serial copy against production rayon — a settled choice), remove_e2e/first_output deleted (duplicate of first_output/remove). Ends three gist series with this PR as the single discontinuity point; saves roughly 15–20 min of the ~80-min daily bench run.
6. wt-perf CLI tests moved in-package (native CARGO_BIN_EXE_wt-perf): the dummy builds.rs is gone and the nextest setup script builds only mock-stub. Note cargo test --test integration no longer runs these four tests; full-workspace runs still do.
7. parse_config returns a SetupConfig enum covering mixed-W-B; the two fixture builders share init_bench_repo.

Merge with main (#3401): the new prune benches and fixtures landed mid-flight in exactly these files; the resolution routes them through the consolidated API — prune-M-U is a SetupConfig::Prune variant, the pair parsing is one shared parse_pair, and prune-real keeps its own cache-managed path (no --path, self-repairing). benches/prune.rs keeps its custom iter_batched arms deliberately: every variant asserts the candidate count from stdout, which bench_wt's shape doesn't express — the exact carve-out the cache-handling docs describe.

Two review passes (correctness + subtraction) then folded in: CacheReport trimmed to its same-context fields (the dropped six duplicated Profile fields or counted cross-context noise the text report never showed), render_table pads by display width (replacing an ASCII-only invariant the new BY CONTEXT table violated), the timeline's instant-event row gained test coverage, and Chrome args dropped the redundant duration_ms.

Decisions surfaced, not taken (from the review passes): (a) wt-perf setup could become --persist-only, dropping the interactive Enter-to-cleanup path — a UX preference; (b) whether the daily benchmark cron's gist time series justifies its remaining ~60 min/day is a cost/value call. Also deferred: measuring whether skeleton/cold adds signal over skeleton/warm before cutting it.

Gate green throughout (4374 tests); clippy --features shell-integration-tests clean; setup/timeline (warm, cold, chrome)/logs profile (text + JSON)/trace all driven end-to-end on a scratch mixed-4-8 repo.

This was written by Claude Code on behalf of max

[worktrunk-bot]

Reviewing as a draft — flagging anything that looks worth a quick fix. Mark ready for a full review.

The refactor is clean and internally consistent — the by_context aggregation, the moved traced/wall timeline computation, the SetupConfig enum, and the bench_wt warm/cold strategy all preserve the prior behavior, and I found no correctness issues. Two documentation-accuracy nits:

• benches/CLAUDE.md (expected-numbers table, the remove_e2e/first_output row) — this row (~86 ms, "single-target validation up to first output") documents the bench variant this PR deletes from benches/remove.rs. It's outside this diff's hunks so I can't attach an inline suggestion; either drop the row or repoint it at the surviving first_output/remove variant in time_to_first_output.rs.

Inline suggestion below for the other one.