Side-panel / new-chat composer stuck at ~80 px — #178 auto-grow inline height overrides the .no-messages fill layout

[sierragolflima]

Summary

In the right-hand side-panel AI chat, the message composer is stuck at roughly 80 px
(≈3.5 lines) and does not grow — whether you type or paste more than ~3.5 lines — even
though the side panel is much taller and has ample empty space above/below the box. This is
a new-chat / side-panel-specific defect, distinct from #178 (which correctly fixed
auto-grow for an ongoing thread with messages).

Screenshot

Steps to reproduce

1. Open the AI chat in the right-hand side panel (a fresh/new chat).
2. Type or paste content longer than ~3.5 lines.
3. Observe: the editable box stays at ~80 px and scrolls internally; it never expands to
   use the visible empty space.

Root cause (code)

The side panel always mounts the new-chat ThreadChatView
(src/MeshWeaver.Blazor.Portal/Chat/ThreadSidePanelContent.razor:65), which runs the view
in its .no-messages state. That state applies a deliberately different composer
layout than a thread-with-messages:

• .no-messages (side panel / new chat): .input-container { flex: 1 1 auto } —
  intended to let the input fill the tall empty slot
  (src/MeshWeaver.Blazor.Portal/Chat/ThreadChatView.razor.css:20-39, per its own comment:
  "the input field grows to occupy the space rather than sitting as a thin bar").
• with messages (main pane): .input-container { flex: 0 0 auto } — a natural-height
  bottom bar, which is the case AI chat composer input too small — no auto-grow, 80 px initial / 200 px max in Blazor #178's auto-grow was written and tested against.

The #178 auto-grow change pins the editor's outer container to an inline
height: 80px; max-height: min(400px, calc(100vh - 280px)); min-height: 80px
(src/MeshWeaver.Blazor/Components/Monaco/MonacoEditorView.razor:158, the AutoGrow
ContainerStyle), applied by
src/MeshWeaver.Blazor.Portal/Chat/ThreadChatView.razor:947-949
(Height="80px" MaxHeight="min(400px, calc(100vh - 280px))" AutoGrow="true").

That inline height: 80px wins over the .no-messages fill intent, so the editable box
sits at ~80 px at the top of a tall flex:1 .input-container, with empty space below —
exactly the reported symptom. The two features (the #178 auto-grow sizing and the
.no-messages fill layout) were never reconciled.

A second, additive possibility (deployment)

The "does not grow at all, even when typing" part can also be aggravated if the
deployment's application assembly MeshWeaver.Blazor.Portal.dll (which carries
AutoGrow="true") predates the #178 fix while the framework static asset is current —
in that case the JS grow handler (onDidContentSizeChange,
src/MeshWeaver.Blazor/Components/Monaco/MonacoEditorView.razor.js:312-339) is never even
attached. The code conflict above is independent and reproducible from current main;
this is only noted so that whoever verifies also confirms the deployed app assembly
includes commit 706d0ff54 (#178).

Expected behaviour

• In the new-chat / side-panel composer, the input should use the available vertical space
  per the .no-messages design — no thin ~80 px box floating in a tall slot.
• Typing or pasting content taller than the box expands the editable area (up to a
  viewport-relative ceiling) and only then scrolls internally — content is never hidden
  while empty space remains.
• The with-messages composer auto-grow (AI chat composer input too small — no auto-grow, 80 px initial / 200 px max in Blazor #178) must remain unchanged.

Proposed fix direction

Reconcile the two behaviours so the AutoGrow inline height does not override the
.no-messages fill. For example: in the .no-messages state let the auto-grow container
use the fill (a flex:1 / height:100% baseline of its slot) rather than the fixed
height:80px, keeping the max-height/scroll cap; or gate the fixed-80 px baseline to the
with-messages state only. Exact approach left to the implementer — the constraint is that
the #178 with-messages auto-grow keeps working.

Acceptance criteria

• In the side-panel new-chat composer, typing/pasting > ~4 lines expands the editable area
  (it does not stay at ~80 px with empty space above/below), up to the viewport cap, then
  scrolls.
• The new-chat composer occupies the available vertical space per the .no-messages design.
• The with-messages composer auto-grow (AI chat composer input too small — no auto-grow, 80 px initial / 200 px max in Blazor #178) is unchanged in the main pane.
• Both main-pane and side-panel surfaces pass the checks.

References

• AI chat composer input too small — no auto-grow, 80 px initial / 200 px max in Blazor #178 (auto-grow for the with-messages composer) — fixed by 706d0ff54; this issue is the
  uncovered new-chat/side-panel case.