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>

presentation/chat/chat_panel_layout.py

@@ -0,0 +1,150 @@
+"""Bố cục khung chat — R08-T06.
+
+Hai cột: mạch hội thoại bên trái, khung tệp đầu ra bên phải. Ô nhập nằm dưới
+CẢ HAI cột — đó là lý do khung tệp đứng cạnh mạch hội thoại mà không làm hẹp
+chỗ gõ. Đặt trong cột chat thì ô nhập co lại mỗi lần có tệp xuất hiện.
+
+Vài widget cố ý được gắn vào một cha ẩn vĩnh viễn thay vì bỏ hẳn: khung tệp
+đầu vào và bảng kế hoạch cũ vẫn còn được gọi ``set_steps``/``add`` ở nơi
+khác. Không có cha thì lần gọi đầu tiên sẽ bật lên thành một cửa sổ nổi lạc
+lõng giữa màn hình.
+
+Cùng kiểu mixin, xem ghi chú ở đầu ``presentation/shell/nav_rail.py``.
+"""
+from __future__ import annotations
+
+from pathlib import Path
+from typing import Any, Dict, List, Optional
+from PySide6.QtCore import Qt, QTimer, Signal
+from PySide6.QtCore import QFileSystemWatcher
+from PySide6.QtWidgets import (
+    QComboBox, QHBoxLayout, QLabel, QMessageBox, QPushButton, QSplitter,
+    QVBoxLayout, QWidget,
+)
+from ...core.worker import AgentWorker
+from ...i18n import on_language_changed, tr
+from ...state import AppContext
+from ...theme import current_palette
+from .chat_bubble_style import ThinkingIndicator
+from .chat_history_widget import ChatView
+from .composer_widget import Composer
+from ...ui.icons import collapse_right_icon, icon as app_icon
+from ...ui.osutil import is_image, open_path
+from ...ui.widgets import CollapsibleSection, CollapseStrip, PlanSection
+
+
+class ChatPanelLayoutMixin:
+    """Dựng bố cục. Trộn vào ChatPanel."""
+
+    def _build_layout(self, root) -> None:
+        """``root`` là QVBoxLayout gốc do ``__init__`` dựng."""
+        # Chat column: transcript expands, the chat box is pinned at the bottom.
+        chat_col = QWidget()
+        cc = QVBoxLayout(chat_col)
+        cc.setContentsMargins(0, 0, 0, 0)
+        cc.setSpacing(0)
+        cc.addWidget(self.chat_view, 1)
+        self.thinking = ThinkingIndicator()   # animated "working…" line while we wait
+        cc.addWidget(self.thinking)
+        self.center_split = QSplitter(Qt.Horizontal)
+        self.center_split.addWidget(chat_col)
+        root.addWidget(self.center_split, 1)
+
+        # The composer spans the whole screen, under BOTH columns — that is how
+        # the drawing lays it out, and it is the reason the files panel can sit
+        # beside the transcript without narrowing what you type into. Inside the
+        # chat column it stopped at the panel's edge and the input shrank
+        # whenever files appeared.
+        composer_wrap = QWidget()
+        cwl = QVBoxLayout(composer_wrap)
+        cwl.setContentsMargins(8, 4, 8, 8)
+        cwl.addWidget(self.composer)
+        root.addWidget(composer_wrap)
+
+        # Right sidebar: Output files only (see below — Input is tracked but
+        # not shown).
+        self.input_section = CollapsibleSection(tr("widgets.input_files"))
+        # No cap: this section owns the whole right panel (its header is
+        # hoisted into io_hdr below), so the list should fill the space down
+        # to the composer instead of stopping at a fixed height with empty
+        # panel below it.
+        self.output_section = CollapsibleSection(tr("widgets.output_files").upper(), max_height=None)
+        # Input files are NOT shown in Cowork's UI anymore — but they're still
+        # fully tracked (add/remove/paths()) exactly as before, since that list
+        # is what gets written into the conversation's own "inputs" field on
+        # save (kept alongside the conversation; nothing here deletes the
+        # user's actual files — the conversation JSON itself only disappears
+        # when the conversation is deleted, same as always). Give input_section
+        # a real, permanently-hidden PARENT (not just "never added to a layout")
+        # so its own internal auto-show-on-add() call can never pop it up as a
+        # stray floating window.
+        self._input_hidden_host = QWidget(self)
+        self._input_hidden_host.setVisible(False)
+        _hh_lay = QVBoxLayout(self._input_hidden_host)
+        _hh_lay.setContentsMargins(0, 0, 0, 0)
+        _hh_lay.addWidget(self.input_section)
+        self.plan_section = PlanSection(tr("widgets.plan_title"))   # live step checklist, above the Files panel
+        # The plan is shown INLINE in the conversation now (see add_plan), so this
+        # legacy right-panel checklist is parked inside the permanently-hidden
+        # host. Without a parent it would pop as a stray top-level "Plan (N)"
+        # window the moment set_steps() made it visible — parenting it here keeps
+        # its set_steps/clear calls truly inert (a hidden ancestor never renders).
+        _hh_lay.addWidget(self.plan_section)
+        self.input_section.activated.connect(self._open_io_item)
+        self.output_section.activated.connect(self._open_io_item)
+        # Right-click a file → Open / "View & AI Edit" (in-app viewer+editor).
+        for section in (self.input_section, self.output_section):
+            section.list.setContextMenuPolicy(Qt.CustomContextMenu)
+            section.list.customContextMenuRequested.connect(
+                lambda pos, s=section: self._io_context_menu(s, pos))
+        self._io_widget = QWidget()
+        iol = QVBoxLayout(self._io_widget)
+        iol.setContentsMargins(6, 6, 6, 6)
+        iol.setSpacing(4)
+        io_hdr = QHBoxLayout()
+        self._io_collapse_btn = QPushButton()
+        self._io_collapse_btn.setIcon(collapse_right_icon())
+        self._io_collapse_btn.setFixedWidth(28)
+        self._io_collapse_btn.clicked.connect(lambda: self._set_io_collapsed(True))
+        self._files_header = QLabel()
+        self._files_header.setStyleSheet("font-weight:600;")
+        # The drawing gives this panel ONE heading — "TỆP ĐẦU RA (3) ›" — and
+        # the section already draws exactly that, count included. A separate
+        # "Files" label above it was the same thing said twice, so the section's
+        # own header moves onto this row and the collapse chevron sits at its
+        # right, where the drawing puts it. _files_header stays for the tabs
+        # that still label their panel, just not in this layout.
+        self._files_header.setVisible(False)
+        io_hdr.addWidget(self.output_section.header, 1)
+        io_hdr.addWidget(self._io_collapse_btn)
+        # The plan now shows INLINE in the conversation (an expandable block whose
+        # steps tick off as they complete), not in this right panel — so it's kept
+        # out of the layout here. The object stays (its set_steps/clear calls are
+        # harmless no-ops on a hidden widget).
+        self.plan_section.setVisible(False)
+        iol.addLayout(io_hdr)
+        bl_host = QWidget()
+        bl = QVBoxLayout(bl_host)
+        bl.setContentsMargins(0, 0, 0, 0)
+        bl.setSpacing(4)
+        bl.addWidget(self.output_section, 1)   # Output only — Input is tracked but hidden; fills down to the composer
+        iol.addWidget(bl_host, 1)
+
+        # Collapsing shrinks the panel to a thin clickable line (not hidden).
+        # The collapse button lives in the panel header; the strip re-expands.
+        self._io_strip = CollapseStrip(tr("chatpanel.expand_files_tooltip"), expand_dir="left")
+        self._io_strip.clicked.connect(lambda: self._set_io_collapsed(False))
+        self._io_strip.setVisible(False)
+        self._io_pane = QWidget()
+        pl = QHBoxLayout(self._io_pane)
+        pl.setContentsMargins(0, 0, 0, 0)
+        pl.setSpacing(0)
+        pl.addWidget(self._io_strip)
+        pl.addWidget(self._io_widget, 1)
+
+        self.center_split.addWidget(self._io_pane)
+        self.center_split.setStretchFactor(0, 1)
+        self.center_split.setStretchFactor(1, 0)
+        self.center_split.setChildrenCollapsible(False)
+        self.center_split.setSizes([820, 220])
+        on_language_changed(self._retranslate_base)