phase10: config.lua example for cfg.norris.{preplanner,executor}

Documents the new Phase 10 / #89 surface for users: when, why, and
how to set cfg.norris.preplanner + .executor + .tasks_max. Notes the
graceful single-model fall-back when preplanner is unset OR fails,
and the design choice that preplan does NOT route via call_broker
(retry would silently swap planning models).

C5: config-only commit; no behavior change.

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

config.lua

@@ -307,6 +307,37 @@ return {
     -- tail is usually the relevant bit); known limitation for
     -- structured tool results. Disable per-model if it bites.
 
+    -- ── Issue #89 / Phase 10: cloud preplanner → local executor split.
+    -- When cfg.norris.preplanner names a model preset, :norris launch
+    -- fires ONE broker.chat against that preset asking for a sequence
+    -- of TASK: <imperative> lines. Parsed list (capped at tasks_max)
+    -- becomes ctx.norris_tasks; the executor model (cfg.norris.executor,
+    -- defaulting to the active :model selection) runs each task with
+    -- the current task shown in the per-step header.
+    --
+    -- Goal: small fast local models are cheap per step but easily
+    -- distracted on multi-step plans; cloud is capable at planning
+    -- but expensive per step. Use cloud ONCE for the plan, local for
+    -- every step. Falls back to single-model Norris (existing
+    -- behavior) when preplanner unset / fails / produces no TASKs.
+    --
+    -- norris = {
+    --     preplanner = "anthropic",   -- model name in cfg.models;
+    --                                 -- this preset is called ONCE per
+    --                                 -- :norris launch. Omit to run
+    --                                 -- single-model (Phase 6 behavior).
+    --     executor   = "fast",        -- model that runs each step.
+    --                                 -- Omit to use the active :model.
+    --     tasks_max  = 16,            -- cap on preplan list size.
+    --     -- preplan_system = "...",  -- override the built-in prompt
+    -- },
+    --
+    -- :cost detail separates norris-preplan and norris rows so you
+    -- can see cloud planning cost vs local execution cost. The
+    -- preplan call does NOT retry via fallback_model (a different
+    -- model = a different decomposition; clean hard-fail to single-
+    -- model is safer).
+
     -- ── Phase 5 context summarization on sliding-window eviction.
     -- Set INSIDE the context = { ... } block above to enable:
     --     context = {