PR #15140: fix(tui): fix invisible slash-command overlays and FormattedText display serialization

• Repository: NousResearch/hermes-agent
• Author: konsisumer
• State: open | merged: False
• Link: https://github.com/NousResearch/hermes-agent/pull/15140

Description (problem / solution / changelog)

Fix two remaining gaps that kept /resume and /model picker overlays invisible in TUI v0.11.0.

What changed and why

• ui-tui/src/components/appLayout.tsx: pass completions={isBlocked ? [] : composer.completions} to FloatingOverlays. When a blocking overlay (session picker, model picker, pager, skills hub) is open, the normal autocomplete dropdown must not also appear. Previously all completions were passed unconditionally, which could cause the dropdown to overlap the picker.
• tui_gateway/server.py: in complete.slash, replace c.display or c.text with to_plain_text(c.display) if c.display else c.text. prompt_toolkit Completion.display is a FormattedText object, not a str; the to_plain_text helper was already imported for display_meta but was not applied to display, causing broken rendering in the TUI completion dropdown.
• tests/test_tui_gateway_server.py: new test test_complete_slash_display_is_plain_string verifies that a FormattedText display value is serialized to a plain str in the RPC response.

How to test

• Start Hermes TUI and run /resume with no argument — the session picker overlay should appear.
• Run /model with no argument — the model picker overlay should appear.
• Type /res in the composer — slash completion dropdown appears; selecting a command should work normally.
• pytest tests/test_tui_gateway_server.py -q — all 56 tests pass including the new one.

What platforms tested on

• macOS on darwin-arm64 (local)

Fixes #15094 Fixes #14907

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Changed files

• tests/test_tui_gateway_server.py (modified, +35/-0)
• tui_gateway/server.py (modified, +1/-1)
• ui-tui/src/components/appLayout.tsx (modified, +1/-1)