Phase-2 preflight execution. PR 1 (#120) added config + CLI flag
plumbing; this PR makes the flags actually DO something — publish every
crate in the plan to an alternate registry, verify visibility, and
emit a `RehearsalComplete` event so the outcome is auditable from
`events.jsonl` alone.

## What's new

- **`EventType` variants** (shipper-types):
  - `RehearsalStarted { registry, package_count }`
  - `RehearsalPackagePublished { name, version, duration_ms }`
  - `RehearsalPackageFailed { name, version, class, message }`
  - `RehearsalComplete { passed, registry, summary }`

- **`RuntimeOptions` fields** (shipper-types):
  - `rehearsal_registry: Option<String>` — resolved from CLI
    `--rehearsal-registry` override OR `[rehearsal] enabled=true + registry=...`
    in `.shipper.toml`. None = rehearsal disabled.
  - `rehearsal_skip: bool` — operator override (loud-warning path).

- **`ShipperConfig::build_runtime_options`** populates the new fields
  with correct precedence (CLI > config > None).

- **`engine::run_rehearsal`** (shipper crate):
  - Fails clean if no rehearsal registry is configured.
  - Fails clean if the rehearsal registry isn't in `opts.registries`.
  - Refuses to rehearse against the same registry as the live target
    (the whole point is a sandbox).
  - Honors `--skip-rehearsal` with a warning; returns non-passing
    outcome so the eventual hard gate (PR 3) can detect it.
  - Sequential (parallel rehearsal not planned — correctness > speed).
  - Stops at first failure, emits `RehearsalPackageFailed` +
    `RehearsalComplete { passed: false, ... }`.
  - Uses the SAME `version_exists` readiness mechanism as live publish
    for the post-publish visibility check.
  - Does NOT touch `state.json` — rehearsal is a pre-publish proof,
    not an execution. Event log only.

- **`shipper rehearse` CLI subcommand** that drives `run_rehearsal`
  and exits non-zero on failure so CI lanes can gate on it.

## Scope — explicitly NOT in this PR

- **Hard gate** wiring `run_publish` → refuse without passing rehearsal
  (#97 PR 3). The event log carries `RehearsalComplete { passed }` ready
  for it, but the live path doesn't check yet.
- **Install / smoke check** against the rehearsal registry (likely PR 3
  or 4; needs a consumer-workspace fixture).
- **Parallel rehearsal** (not planned).
- **plan_id binding** of rehearsal outcome (needed by PR 3's hard gate;
  simpler to add alongside the gate itself).

## Tests

6 unit tests in `engine::tests`:
- Errors cleanly with no rehearsal registry.
- Errors cleanly when rehearsal == live target.
- Errors cleanly when the named registry isn't configured.
- `--skip-rehearsal` returns immediately, no events written.
- Happy path emits Started + PackagePublished + Complete(passed=true).
- Cargo-failure path emits PackageFailed + Complete(passed=false).

CLI snapshots for `help_text`, `help_root`, `no_subcommand_error`
regenerated to reflect the new `rehearse` subcommand.

…sal flags

* feat(yank): shipper yank <crate>@<version> (#98 PR 1)

First primitive of the Remediate pillar (#98). Wraps `cargo yank` as
containment, not undo — existing lockfile pins stay pinned; the yank
only prevents NEW resolves against that version.

- ops/cargo: cargo_yank(workspace, name, version, registry, lines, timeout)
  mirrors the cargo_publish invariants (non-default registry passthrough,
  timeout polling, output redaction + tailing via output-sanitizer).
- CLI: `shipper yank --crate <name> --version <ver> --reason <why>` emits
  a PackageYanked event to <state_dir>/events.jsonl capturing the reason
  and the cargo exit code; surfaces a loud operator warning about
  containment semantics and the `cargo update -p <name>` remediation step
  for downstream consumers.
- types: PackageYanked event variant (crate_name, version, reason, exit_code).
- tests: three fake-cargo unit tests in ops/cargo (args passthrough,
  crates-io registry omission, non-zero exit propagation) + a yank
  --help snapshot in e2e_expanded.

Scope-limited on purpose: follow-on PRs under #98 compose this into
`shipper plan-yank` (reverse-topological containment plan) and
`shipper fix-forward` (patch-and-republish).

* test(yank): regenerate CLI help snapshots after PR #120 landed rehearsal flags

Phase-2 preflight execution. PR 1 (#120) added config + CLI flag
plumbing for rehearsal registry; this PR makes the flags actually DO
something — publish every crate in the plan to an alternate registry,
verify visibility, and emit a RehearsalComplete event so the outcome
is auditable from events.jsonl alone.

- EventType variants: RehearsalStarted / RehearsalPackagePublished /
  RehearsalPackageFailed / RehearsalComplete
- RuntimeOptions fields: rehearsal_registry, rehearsal_skip
- ShipperConfig::build_runtime_options populates with CLI > config > None precedence
- engine::run_rehearsal: sequential, stops at first failure, emits events,
  does not touch state.json (pre-publish proof, not execution),
  verifies post-publish visibility via the same mechanism live publish uses,
  refuses to rehearse against the live target registry
- shipper rehearse CLI subcommand

Also regenerates the matching CLI snapshots (help_text, help_root,
no_subcommand_error).

…2) (#127)

Phase-2 preflight execution. PR 1 (#120) added config + CLI flag
plumbing for rehearsal registry; this PR makes the flags actually DO
something — publish every crate in the plan to an alternate registry,
verify visibility, and emit a RehearsalComplete event so the outcome
is auditable from events.jsonl alone.

- EventType variants: RehearsalStarted / RehearsalPackagePublished /
  RehearsalPackageFailed / RehearsalComplete
- RuntimeOptions fields: rehearsal_registry, rehearsal_skip
- ShipperConfig::build_runtime_options populates with CLI > config > None precedence
- engine::run_rehearsal: sequential, stops at first failure, emits events,
  does not touch state.json (pre-publish proof, not execution),
  verifies post-publish visibility via the same mechanism live publish uses,
  refuses to rehearse against the live target registry
- shipper rehearse CLI subcommand

Also regenerates the matching CLI snapshots (help_text, help_root,
no_subcommand_error).