Enforce the token cap, and treat a spent budget as an interruption

Exceeding a LiteLLM spend limit takes external models away for the
rest of the day, which makes three existing gaps consequential rather
than untidy.

- A13 calls the delegation caps hard on "turns, tokens, and wall
  clock", and the module docstring repeated it, but the token cap was
  decoration: nothing counted, and result.tokens was always zero. It
  is now metered from the usage the provider reports, so a confused
  delegate cannot spend a day's allowance. A5 keeps the *money* cap on
  the LiteLLM key, which is a different thing; this is a scope cap
- The normalized route sent no ceiling at all, so truncation detection
  there had nothing to detect against. Both routes now send one
- A budget refusal is recognised distinctly. It is not a rate limit:
  retrying cannot help, so the planner no longer burns a second call
  to fail identically

And a delegation cut off by an exhausted budget is now "interrupted"
rather than "failed", which preserves its branch and leaves its intent
pending. The work on that branch may be perfectly good; discarding it
because the budget ran out would throw away work for a reason that has
nothing to do with the work. A3's resume rule already knows how to
pick such a delegation back up.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

nisse-dev/src/nisse_dev/planner.py

@@ -13,7 +13,7 @@ from typing import Any
 
 from nisse_dev.canonical import AssistantText, ToolCall, ToolResult
 from nisse_dev.control import AskHuman, PlanningError, SubmitPlan
-from nisse_dev.llm import LLMClient, LLMError, RoleMap
+from nisse_dev.llm import BudgetExhausted, LLMClient, LLMError, RoleMap
 from nisse_dev.state import StateStore
 
 # Plans may be executed by a materially weaker model, which cannot
@@ -125,6 +125,11 @@ class LLMPlanningAgent:
         output is observable, never the model's own claim)."""
         try:
             return self._turn(model, system), None
+        except BudgetExhausted:
+            # Retrying cannot help: the budget will not reappear within a
+            # turn. Surface it now so the operator is told rather than the
+            # loop spending a second call to fail identically.
+            raise
         except LLMError as exc:
             return None, str(exc)