Runner-driven dispatch for every task

[slowdini]

Part of #244 (full-codebase eval testbed). No dependencies — startable today.

Why

Today only tasks declaring scripted turns are runner-driven: run_task
(src/cli/run/conversation.rs:89-93) errors out if a task has none. Every one-shot task is
dispatched by a human or an agent following the recipe in profiles/shared/runbook.md.

#244 wants real tasks with a dynamic number of turns, run enough times to be statistically
meaningful. That is not drivable by hand, and dynamic turns are impossible without the runner in the
loop. There is also no per-dispatch timeout anywhere — execute_round
(src/cli/run/conversation.rs:367-387) runs to completion, so one hung task hangs the campaign.

Decision taken on #244: the runner drives every dispatch.

Scope

• Drop dispatch-task's "must declare scripted follow-up turns" precondition so one-shot tasks run
  through the same driver, which already handles turn 1, native session resume, transcript parsing,
  and the conversation.json completion artifact.
• Add eval-magic dispatch --iteration N [--jobs K] [--task-index …]:
  • --jobs concurrency (each env is private, so tasks are independent).
  • Per-task timeout with the timeout recorded as a task outcome, not a crash.
  • Recorded failures rather than aborting the campaign.
  • Resume on rerun — completed tasks are skipped unless --overwrite.
• Rewrite profiles/shared/runbook.md and each harness's next_steps / manifest templates around
  the single command. Golden artifacts under tests/golden/ pin this output and must be updated.

Files

• src/cli/run/conversation.rs — the driver
• src/cli/run/dispatch.rs, src/cli/commands/run.rs
• src/cli/args.rs, src/cli/help.rs
• profiles/shared/runbook.md, harnesses/*.toml
• tests/golden/

Acceptance criteria

• A one-shot task and a multi-turn task both complete through eval-magic dispatch.
• --jobs 4 runs four tasks concurrently without cross-task interference.
• A task exceeding its timeout is recorded as timed out; the rest of the campaign completes.
• Rerunning dispatch skips completed tasks and reruns only failures.
• RUNBOOK.md describes one dispatch command; golden tests updated to match.

Note

This is the largest single behavioural change in #244 and it unblocks the dynamic-turn work.

Cross-cutting requirements

• Mode B parity. Acceptance must hold for both Mode::NewSkill and Mode::Revision
  (src/core/types.rs:225), and the snapshot/promote path (src/workspace/snapshot.rs,
  src/workspace/promote.rs) must keep working against codebase-backed iterations.
• Provenance reaches the report. Source + resolved SHA must land in conditions.json, each
  run.json, benchmark.json, and the BASELINE.md built by promote.rs:231 — not just in the
  workspace.

Verification

cargo fmt --check && cargo build && cargo test && cargo clippy --all-targets -- -D warnings

Implementation requires the slow-powers:working-with-tdd skill.

Parent: #244

[slowdini]

Platform support target: Windows requires WSL

Windows-native support is deprecated. The supported platforms are Linux and macOS, with Windows supported through WSL. Git Bash remains the transitional path until the removal tracked in #275, but nothing new should be built to accommodate it. The tiers are recorded under Platform support in docs/developer_overview.md (#274).

Recording it here because this ticket rewrites the surface that carries the largest Windows accommodation in the tree, and should aim at the end state rather than preserving accommodations already slated for removal.

What that means here

Removing the recipe surface's Windows handling as part of the rewrite is in scope; porting it forward is not.

• The tr -d '\r' strips in render_parallel_dispatch_recipe and render_judge_dispatch_recipe (src/adapters/cli_command.rs) exist because jq's native Windows build writes CRLF. They go with the recipes.
• POSIX_RECIPE_TOOLS and require_posix_toolchain (src/core/runtime.rs) preflight jq, xargs, tr, and wc for those recipes. With the runner dispatching directly, the jq requirement goes with them and preflight_posix_tooling (src/cli/run/orchestrate/shell.rs) shrinks to whatever the driver still needs.
• recipes_strip_the_carriage_return_a_windows_jq_emits and judge_recipe_counts_verdicts_when_jq_emits_crlf pin those strips. Both are recipe tests — they retire with the recipes rather than being ported.

What stays

execute_round (src/cli/run/conversation.rs) spawns sh -c because harness exec_templates are POSIX command lines in the descriptors. Runner-driven dispatch does not remove the shell requirement, so posix_shell() stays — minus its Git for Windows discovery, which #275 removes separately.

Do not add Windows-native handling to the new dispatch path.