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

nisse-core/README.md

@@ -2,7 +2,10 @@
 
 The shared library both Nisse agents sit on (Part L of the architecture).
 
-It does not exist as code yet: it is extracted from `nisse-dev` once that agent
-works, at step 10 of the build order — a package split within this repository.
-Until then this directory is a placeholder holding the seam the extraction will
-land on.
+Most of it still lives in `nisse-dev`, to be extracted as `nisse-ops` arrives.
+What is here so far:
+
+- `nisse_core.actions`: actions by their effects (P3, P4, L4). The `Action`
+  and `Verdict` types, and static reading of shell commands, which each
+  agent's fast-path rules build on (`nisse-dev`'s are in
+  `nisse_dev.loop.actions`).