Feature/delta team/epic r04 (#7)

## Summary

epic r04 - begin refactor

## Change Type

- [x] Cowork feature
- [ ] Bug fix
- [ ] Core AI contribution
- [ ] Test / hardening
- [ ] Performance
- [ ] Documentation

## Related Work

Cowork Task:

Core Repo: http://34.143.229.138/gitea-admin/fsg-ai-core-assets

Core AI Issue:

Core Task:

Related PR:

## Scope

What is intentionally included?

What is intentionally NOT included?

## Validation

- [ ] Unit tests
- [ ] Integration tests
- [ ] Manual verification
- [ ] Regression check

Commands / evidence:

## Security Impact

Permission / credential / network / customer data impact:

## Compatibility

- [ ] No breaking change
- [ ] Breaking change documented

## Reviewer Notes

Anything Cowork reviewers should pay attention to.

---------

Co-authored-by: Anh Tran Nguyen Minh <anhtnm1@fpt.com>
Co-authored-by: Huong Le Thi Thien <huongltt35@fpt.com>
Co-authored-by: Nam Pham Dinh Thanh <nampdt@fpt.com>
Co-authored-by: Vu Dam Tuan <vudt15@fpt.com>
Co-authored-by: Hiep Ha Van <hiephv3@fpt.com>
Co-authored-by: Lam Hoang Van <lamhv7@fpt.com>
Reviewed-on: #7
Co-authored-by: Duy Le Huu <duylh19@fpt.com>

domain/agents/agent_result.py

@@ -0,0 +1,86 @@
+"""What one finished turn produced (R04-T03).
+
+The outcome of a turn is currently spread over three shapes: ``run_cowork``
+returns the mutated message list, ``task_executors._run_agent`` returns a
+``(answer_text, timed_out, incomplete_reason)`` tuple, and the UI reconstructs
+the rest (did it get cancelled? did it hit the ceiling?) from side effects. Each
+caller therefore knows a slightly different amount about the same turn.
+
+:class:`AgentResult` is the single answer. Frozen, like the request that started
+the turn, so a result cannot be edited into disagreeing with what actually
+happened.
+
+Layer rules (``docs/architecture/ADR-001-layered-architecture.md``): domain
+layer — standard library plus sibling domain types only.
+"""
+
+from __future__ import annotations
+
+from dataclasses import dataclass
+from typing import Any, Dict, Tuple
+
+from .agent_event import PlanStep, TurnCompletedEvent
+
+
+@dataclass(frozen=True)
+class AgentResult:
+    """The outcome of one conversation turn."""
+
+    # The conversation AFTER the turn (system prompt, history, the new user
+    # message, every assistant reply and tool result).
+    messages: Tuple[Dict[str, Any], ...] = ()
+    steps_used: int = 0                    # provider calls this turn consumed
+    cancelled: bool = False                # the user pressed Stop
+    budget_exhausted: bool = False         # stopped at effective_max_steps
+    # The agent's final checklist, so a caller can ask "did it really finish?"
+    # (``core/plan.py::plan_incomplete_reason``) without replaying the events.
+    plan_steps: Tuple[PlanStep, ...] = ()
+    # Non-empty when the turn ended on a failure. A string rather than the
+    # exception: the domain layer must not depend on where the error came from,
+    # and the message is what every consumer (bubble, error.txt, audit) shows.
+    error: str = ""
+
+    def __post_init__(self) -> None:
+        """Freeze the collections the runtime hands over.
+
+        Both arrive as live lists that the caller keeps appending to after the
+        turn (the UI merges messages back into its own history), so copying here
+        is what keeps a result a record rather than a moving target.
+        """
+        object.__setattr__(self, "messages", tuple(self.messages or ()))
+        object.__setattr__(self, "plan_steps", tuple(self.plan_steps or ()))
+
+    @property
+    def final_text(self) -> str:
+        """The answer to show the user.
+
+        Scans backwards for the last assistant message with real content, which
+        is not the same as ``messages[-1]``: a turn that was cancelled or that
+        ran out of steps mid-loop ends on a tool message, and a reasoning-only
+        reply leaves a blank assistant message behind. Same rule as
+        ``core/task_executors.py::_last_assistant_text``, which this replaces.
+        """
+        for message in reversed(self.messages):
+            if message.get("role") == "assistant" and (message.get("content") or "").strip():
+                return str(message["content"])
+        return ""
+
+    @property
+    def ok(self) -> bool:
+        """Whether the turn ran to a normal end.
+
+        Hitting the step ceiling still counts as ok: the agent did work and
+        produced an answer, it just was not allowed to keep going — which the
+        transcript says in its own note rather than by failing the turn.
+        """
+        return not self.error and not self.cancelled
+
+    def to_turn_completed_event(self) -> TurnCompletedEvent:
+        """The end-of-turn event carrying this outcome to subscribers."""
+        return TurnCompletedEvent(
+            final_text=self.final_text, steps_used=self.steps_used,
+            cancelled=self.cancelled, budget_exhausted=self.budget_exhausted,
+        )
+
+
+__all__ = ["AgentResult"]