M4.1: toolchain preflight

A model works out and sets up what a project needs on its build VM;
code makes sure that happens, bounds it and checks the result (D3).

- Before each driver run on a project, one round trip checks the build
  VM: the harness's own baseline (missing: the item waits, a template
  problem), the workspace clone (missing: cloned again and said; the
  item resumes from what it pushed) and a per-project marker.
- No marker (a new project, a new or wiped VM): the item's driver model
  runs a bounded preflight first, with its own prompt, the execution
  tools (screened as ever) and toolchain_ready. The harness runs each
  reported version command itself (version-shaped commands only, even
  from the marker, which the model's commands could edit) and writes
  the marker. Gaps and an unfinished preflight are facts and work goes
  on; the thread hears only of installs and gaps. A rebuilt VM starts
  from the last toolchain.
- Later runs check the versions again; a change is a fact and a thread
  line. The PR body says what the work was tested with.
- A changed host key is its own failure (HostKeyChanged): the item
  waits for the operator's `trust new host key`, which drops the pin;
  then the VM is set up again.
- A prompt line: install what the work needs on the build VM, say why,
  and put lasting needs in the project's own pins.
- tuning.preflight: max_turns, command_timeout_s.
- The property walk gains a VM wipe and ready_before_work (checked
  against a mutant that skips preflight); parked_work_safe accepts that
  a wipe loses what wasn't pushed (D3).

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

nisse-dev/src/nisse_dev/config.py

@@ -98,6 +98,12 @@ class DriverTuning:
     failure_limit: int = 2
 
 
+@dataclass(frozen=True)
+class PreflightTuning:
+    max_turns: int = 20  # model calls a preflight run may make (M4.1)
+    command_timeout_s: int = 900  # one command in it: installs take a while
+
+
 @dataclass(frozen=True)
 class ExpertTuning:
     consult_budget: int = 3
@@ -134,6 +140,7 @@ class LoopTuning:
 @dataclass(frozen=True)
 class Tuning:
     driver: DriverTuning = field(default_factory=DriverTuning)
+    preflight: PreflightTuning = field(default_factory=PreflightTuning)
     expert: ExpertTuning = field(default_factory=ExpertTuning)
     delegation: DelegationTuning = field(default_factory=DelegationTuning)
     tools: ToolsTuning = field(default_factory=ToolsTuning)