Give each role its own view of the transcript (M1.2)

A model no longer reads another role's turns as its own (#78). The log
stays one record per work item; what a role is shown is projected from
it by Transcript.view() (views.py), which the planner, executor and
helper now build their context from:

- own events unchanged;
- operator messages labelled with their channel, e.g.
  [operator, Matrix] or [operator, comment on PR #165];
- orchestrator facts (a new `fact` event) as [orchestrator] statements;
- the executor sees a helper's handback as [helper report], not its turns;
- a helper sees the approved plan and the executor's milestone work as
  one-line narration;
- the planner sees no other role's work at all.

The orchestrator now writes facts at the points the models must know
about: work item opened, plan approved or rejected, milestone started,
finished or stopped, published (with PR number and URL) or not, review
comment answered, next milestone, task completed or abandoned.

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/delegation.py

@@ -33,6 +33,7 @@ from nisse_dev.canonical import (
     AssistantText,
     DelegationCompleted,
     DelegationStarted,
+    PlanSubmitted,
     StoredEvent,
     ToolCall,
     ToolResult,
@@ -328,6 +329,7 @@ class Delegation:
         touched: set[str] = set()
         did_work = False
         spent = 0
+        after = _plan_scope(transcript)
 
         for turn in range(self._caps.turns):
             if self._cancel.requested:
@@ -350,7 +352,7 @@ class Delegation:
                 )
             try:
                 produced = self._client.complete(
-                    transcript.read(),
+                    transcript.view(after=after),
                     tools=DELEGATE_TOOLS,
                     model=self._model,
                     system=system,
@@ -580,6 +582,16 @@ def delegation_verdict(
     return "resume"
 
 
+def _plan_scope(transcript: Transcript) -> int:
+    """Where the helper's view begins: at the approved plan the work is under,
+    so it sees the plan and this milestone, not earlier ones (L6)."""
+    latest = 0
+    for stored in transcript.read():
+        if isinstance(stored.event, PlanSubmitted):
+            latest = stored.id
+    return max(latest - 1, 0)
+
+
 def _completed_after_start(events: list[StoredEvent]) -> bool:
     """True when the last delegation event in the log is a completion."""
     for stored in reversed(events):