…er-platform + per-source drafts)

Unify two complementary-but-separate ideas — per-platform model overrides
and per-source-identity model overrides — into one match-based router.
``model.routes`` is a list of ``{match, model, provider, api_key, ...}``
entries; each ``match`` is a subset predicate against a context dict of
``{platform, source_kind, ...}`` built by the caller. First match wins;
no match leaves the base model untouched.

    model:
      default: my-fast-model
      routes:
        - match: { source_kind: owner }        # owner everywhere
          model: my-strong-model
          api_key: sk-owner
        - match: { platform: hub }             # all hub peers
          model: my-fast-model
        - match: { source_kind: cron }
          model: my-fast-model
        - match: { platform: discord, source_kind: stranger }  # compound
          model: some-other

Backwards-compatible shorthand — both forms synthesize ``routes`` entries
internally:

    model.platforms.<name>:       # existing per-platform shorthand
    model.by_source.<kind>:       # per-source shorthand

Explicit ``routes`` always evaluate first; legacy shims run last, so an
explicit route always wins over an equivalent legacy entry.

Hook points:

- ``agent.smart_model_routing.apply_route`` — pure helper, normalizes
  legacy shorthand, iterates routes, returns ``(model, runtime_kwargs)``.
- ``GatewayRuntime._classify_source_kind(source)`` — classifies
  owner / hub_peer / stranger via home-channel match + platform-value
  string. No dependency on a specific ``Platform.HUB`` enum member.
- ``GatewayRuntime._build_routing_context(source)`` — assembles the
  context dict consumed by ``apply_route``.
- ``GatewayRuntime._resolve_session_agent_runtime`` calls ``apply_route``
  as the final layer, below session ``/model`` overrides and above base
  config. Silent fallback on exception — never blocks a turn.
- Cron scheduler applies with context ``{platform: cron, source_kind:
  cron}`` after runtime resolution and before AIAgent construction.
- HermesCLI applies with context ``{platform: cli, source_kind: owner}``
  in ``_resolve_turn_agent_config``.

This supersedes the earlier ``feat/model-routing`` branch that was cut
before upstream NousResearch#12732 wholesale-removed the separate ``smart_model_routing``
cheap-model router. This rewrite drops the obsolete ``resolve_turn_route`` /
``cheap_model`` integration and lands ``apply_route`` as a standalone
feature on a new ``agent/smart_model_routing.py`` file.

Tests: 14 new unit tests covering the matcher (empty context / no routes
/ platform match / source_kind match / compound match / first-match-wins
/ partial override / empty-value rejection / missing context key / null
config) plus legacy shims (platforms string / platforms dict /
by_source). All pass. No regressions in tests/gateway/, tests/cron/,
or tests/agent/ beyond 12 pre-existing upstream-main failures (dingtalk,
matrix, agent_cache) unrelated to this change.

Supersedes NousResearch#7297 (feat/per-platform-model) and the prior draft at NousResearch#12227
(feat/per-source-model). ``model.platforms.*`` configs keep working via
the legacy shim, so deployments on NousResearch#7297 need no migration.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

…g), drop NousResearch#7297, add NousResearch#12207

- Add rows for NousResearch#12234 (match-based model routing, supersedes NousResearch#7297 and draft NousResearch#12227)
  and NousResearch#12207 (compound-background-subshell-leak).
- Move NousResearch#7297 into a new 'Closed / superseded' section; note the branches
  (feat/per-platform-model and feat/per-source-model) are already deleted from origin.
- Update rebase workflow: swap the feat/per-platform-model line for feat/model-routing,
  add fix/compound-background-subshell-leak.
- Update the fork-main rebuild section: document that octopus strategy fails on
  adjacent-region additions and switch the documented command to a sequential-merge
  loop. Note the recurring conflict site (_classify_source_kind vs _is_owner_source)
  and the union-resolve strategy for it.
- Add PR-specific note for NousResearch#12234 covering the helper, classifier, legacy shim, and
  rebase-conflict guidance.