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Deepen pyte vs GoPyte capture requirements

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@@ -400,7 +400,7 @@ Not yet started. This would be a separate project (`textual-webterm-go`) providi
## pyte vs GoPyte: Thorough Comparison
This section compares the Python **pyte** terminal emulator and the Go **GoPyte** emulator (per their upstream documentation/README). The focus is on capture accuracy, Unicode handling, performance expectations, and integration risk for textual-webterm.
This section compares the Python **pyte** terminal emulator and the Go **GoPyte** emulator (per their upstream documentation/README). The focus is on capture accuracy, Unicode handling, performance expectations, and integration risk for textual-webterm. Where GoPyte details are unclear, we call them out explicitly as validation items.
### Feature Matrix (Capture-Relevant)
@@ -412,20 +412,24 @@ This section compares the Python **pyte** terminal emulator and the Go **GoPyte*
| **Scrollback/history** | HistoryScreen (configurable) | Built-in scrollback (claims) | Semantics may differ; check memory cost. |
| **Resize behavior** | Resizes + cursor + dirty state | Resizes + content (claims) | Must preserve content on resize. |
| **SGR attributes** | Bold/underline/reverse/color | SGR attrs (claims) | Verify italics, faint, strikethrough. |
| **Underline styles** | Basic underline | Unknown | Double/curly underline may be missing. |
| **Color depth** | ANSI + 256 + (truecolor in practice) | ANSI + 256? (verify) | Truecolor required for accurate screenshots. |
| **DEC special graphics** | Supported (line drawing) | Unknown | Box-drawing is critical for TUIs. |
| **Character sets (G0/G1)** | Supported | Unknown | Needed for legacy line-drawing. |
| **Scroll regions** | Supported | Unknown | Needed for curses-style UI. |
| **Insert/delete (IL/DL/ICH/DCH)** | Supported | Unknown | Affects screen fidelity during updates. |
| **Tabs / tab stops** | Supported | Unknown | UI alignment depends on tabs. |
| **Wrap / origin modes** | Supported | Unknown | Impacts cursor positioning and layout. |
| **Autowrap/origin modes** | Supported | Unknown | Impacts cursor positioning and layout. |
| **Cursor save/restore** | Supported | Unknown | Common in TUIs and prompts. |
| **Cursor visibility/style** | Basic visibility | Unknown | Useful for accurate snapshots. |
| **Erase semantics (ED/EL)** | Supported | Unknown | Correct clearing is vital for screenshots. |
| **Unicode width** | wcwidth-style width | go-runewidth | Width differences can misalign SVG. |
| **Combining marks / ZWJ** | Unicode-aware | runewidth-based | Emoji sequences may differ in width. |
| **Dirty tracking** | Exposes dirty set / DiffScreen | Unknown | Needed for efficient screenshot caching. |
| **Images (sixel/kitty)** | Not supported | Not supported | Not required, but a capture limitation. |
| **Performance** | Python, moderate | Go, claims high throughput | Benchmark under heavy output. |
| **API stability** | Mature, widely used | Newer, smaller ecosystem | Risk of breaking changes. |
| **Test maturity** | Established | Claimed high coverage | Must run our own parity suite. |
| **Test maturity** | Established | Claims high coverage | Must run our own parity suite. |
### Unicode & Emoji Handling (Critical for SVG Capture)
@@ -465,21 +469,35 @@ We depend on the emulator for **accurate snapshot state**, not just live display
- **Dirty tracking or diffability** to avoid re-rendering unchanged screens.
- Reliable **color mapping** (ANSI 16 + 256 + truecolor).
- Correct **DEC line drawing** (box-drawing characters).
- Correct **erase semantics** (ED/EL) to avoid stale cells.
If any of these are missing, screenshots will be wrong or expensive to compute.
### Capture-Enhancing (Nice-to-Have) Features
These aren’t required for parity, but would improve capture quality or UX:
- **OSC 8 hyperlink metadata** to annotate clickable URLs in SVG output.
- **Underline styles** (double/curly) for richer text attributes.
- **Cursor style/shape** metadata for accurate snapshots.
- **Grapheme cluster awareness** (emoji sequences treated as single cells).
- **Structured diffs** from emulator (explicit dirty regions instead of full screen).
### Known Gaps / Validation Checklist
Before relying on GoPyte for parity, verify:
- [ ] Full-screen app behavior (vim, htop, less) with alt screen.
- [ ] DEC line drawing / special graphics set (box-drawing correctness).
- [ ] Character set switching (G0/G1) for legacy graphics.
- [ ] Scroll regions (DECSTBM) and origin mode behavior.
- [ ] Insert/delete line/char (IL/DL/ICH/DCH) correctness.
- [ ] Tab stops and tab clear (alignment in TUIs).
- [ ] SGR coverage: bold/underline/italic/reverse + 256/truecolor.
- [ ] Underline styles, faint, strikethrough.
- [ ] Unicode width parity with pyte (emoji + CJK samples).
- [ ] Cursor save/restore (DECSC/DECRC) and visibility toggles.
- [ ] Erase semantics (ED/EL) and autowrap correctness.
- [ ] Resize correctness (content preservation, cursor placement).
- [ ] Performance at high output rates (100k+ lines, low latency).