M3.1: action classes and the fast path

Every execution tool call, the driver's and a helper's, gets a verdict
from code before it runs (P3, P4, D6).

- nisse_core.actions, nisse-core's first code: Action and Verdict, and
  reading shell commands statically, segment by segment (cd, wrappers,
  sh -c). What can't be read that way is unknown; a line is as bad as
  its worst command.
- nisse_dev.loop.actions, the rule table: reading, checks and tests are
  harmless; workspace edits, local git and installs on the build VM are
  contained; pushing, other hosts, uploads, publishing, the forge's own
  tools, deleting outside the workspace and wrecking the VM are
  dangerous; changing branches by hand is refused (the harness owns
  branches) with a pointer to the milestone tools.
- A dangerous call isn't run. The item waits on the operator with a
  question rendered from the action, and `allow` lets exactly that
  action run once. A helper can't ask, so it is refused and told to
  hand back. Unknown actions run, logged, until the classifier (M3.2).
- Every verdict is an action_verdict event, which no model sees, and an
  oplog line; `details` shows the counts and every action not simply
  run.
- The property walk gains dangerous_only_when_allowed (checked against
  a mutant that doesn't use the allow up); the slice e2e checks every
  call was judged and none needed an allow.

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01PPQ14L3LikyefCMFBqEbKE

docs/Architecture.md

@@ -738,6 +738,9 @@ Installing on any other host is dangerous.
 | Contained (in scope) | Editing the workspace; milestone branches, pushes and PRs; commenting on its issues and PRs; filing agreed issues (D1); changing its build VM (D3) |
 | Dangerous | Merging to the default branch (unless the trust dial allows), deleting remote branches or others' work, changing repository settings, anything outside the item's repository or build VM |
 
+Changing branches by hand is neither: it is refused, with a pointer to the
+milestone tools, since the harness owns branches (D4).
+
 ### D7. Deployment and isolation
 
 **The agent** is a container on the agent host (X1) with its state, secrets and API