v1.11.0 — dry-run checks model slugs

Upgrading — dry-run now makes one network call

dry-run used to touch the network zero times. It now issues a single free, unauthenticated
GET https://openrouter.ai/api/v1/models to check your model slugs. Nothing else about the run
changed: no new spend, no new failure mode, same exit codes. (The one cosmetic difference: building
the HTTP opener makes the pre-existing [proxy] detected env proxy line appear on stderr, where
dry-run previously never built one.)

• What you must do: nothing, if that call is fine in your environment.
• If it is not — air-gapped, egress-filtered, or you simply do not want the call — pass
  --no-model-check. That is the complete opt-out; the rest of dry-run is unaffected.
• What you will see if the call cannot complete: one line saying the check was skipped, and the
  dry run proceeds. A refused connection returns in milliseconds; a blackholed one burns the 5s
  socket timeout. That 5s does not bound DNS: socket.getaddrinfo is outside urllib's timeout,
  so a resolver that silently drops the query adds the system resolver's own timeout on top — 20s on
  one machine whose resolver could not be reached, where the same command on 1.10.0 took 0.1s. That
  figure is the operating system's resolver timeout, not something this code sets, so treat it as an
  example rather than a bound. If your egress filters DNS rather than refusing connections, use
  --no-model-check.
• Programmatic callers: dry_run() itself defaults to model_check=False, so importing and
  calling it never reaches the network. Only the CLI opts in.

Added

• dry-run now checks your model slugs against OpenRouter's live list. The README has told
  people "model IDs churn fast; verify once with dry-run" since the beginning, and dry-run
  verified nothing — it printed whatever slug the config contained. It now fetches
  GET /api/v1/models (free, and no Authorization header: the endpoint does not need a key,
  so none is sent) and marks each comparable api link OK / UNKNOWN / MISSING. A retired or mistyped
  slug is visible before the run starts, instead of surfacing as a 400 on one seat after the other
  seats have already been billed.

  Links it cannot honestly compare are marked skip, never guessed at: cli and subagent seats do
  not use OpenRouter slugs at all, and a custom base_url or a non-openrouter protocol has its
  own model namespace — judging those against OpenRouter's list would be all false alarms, which is
  worse than not checking.

  Which links those are is decided exactly the way resolve_channel decides it: the main link by the
  member's own channel, a fallback by the fallback's own channel (absent means api), never by
  the value a fallback inherits from its member. Getting that backwards is what v1.7.0's A1 did — it
  judged the channel off the merged view and refused legal configs, and v1.7.1 shipped the same day to
  undo it. Here the same mistake fails the other way: a cli seat whose fallback omits channel really
  does run as an api link, and judging it off the merge would silently mark it skip — exactly the
  case this feature exists for, since that link sends the member's auggie-side model name to
  OpenRouter. The merged view is still what supplies the link's model, protocol and base_url.

  The check is fail-soft: offline, blocked at the egress, endpoint moved or reshaped, it prints
  one line and the dry run continues with its exit code unchanged — that now includes the judging
  step, not just the fetch, so a config field of an unexpected type degrades the check instead of
  taking down the dry run. The socket timeout is 5s (a refused connection fails in milliseconds, a
  blackholed one burns it); DNS resolution is not covered by it. dry-run is the command SKILL.md
  has the arbiter run in front of the user, which is why the bound matters. --no-model-check turns it off entirely, and the
  dry_run() function defaults to off so that importing it never reaches the network — the
  decision to make that GET belongs to the CLI boundary, and the test suite stays offline.

Fixed

• An api link with no model now says so. call_model indexed cfg["model"] directly, so the
  seat died on a KeyError that _dispatch_channels caught and reported verbatim: the user's
  error field read 'model' [unknown], which names neither the seat's problem nor its fix, and
  the unknown class polluted the error table SKILL.md teaches the arbiter to read. It now raises
  the same PermanentError shape the cli branch uses when its binary is missing from PATH
  (err_class=startup, with a hint), because both are the same thing: a link whose precondition is
  absent, which cannot be attempted at all.

  No new rejection. validate_config still accepts an api member without a model — that is
  pinned by test_validate_config_accepts_valid, and adding the gate a reviewer proposed breaks 22
  tests, 4 of them accepts_* contract tests. A single-model OpenAI-compatible gateway behind
  base_url is also a legitimate reason to omit it. The link still falls through to the next
  fallback exactly as before; only the message and the class changed. Rationale is recorded in
  tasks/specs/model-preflight.md so the gate is not proposed a third time.

Tests 372 → 427.