Statusline

The statusline renderer is a single-pass terminal painter with hand-tuned column math. Most bugs here are silent — wrong by one column, invisible icon, dropped byte through an Edit round-trip. This skill exists to make those bugs loud.

Architecture map

claude/statusline_command.py is a 4-line shim into the yas package under claude/yas/ (app.py/layout.py/renderer.py/… at top level, info/ for data sources, render/ for pure painting/maths). Full per-module map, entry points, and the "where to make a change" table live in ARCHITECTURE.md — read it before adding a module, a data source, or a new row/border/gradient kind; skip it for a same-module tweak.

Pre-edit checklist

Run all four before editing:

1. Read CONTEXT.md at repo root. The terms Billed Input, Cache Read, Output, Day Total, Context Window Size, Compaction-Risk Zone, Five-Hour Limit, Seven-Day Limit are canonical — don't rename or alias them in code without a paired update.
2. Catalogue PUA glyphs on touched lines. Scan the package (glyphs can appear in any module, though most are hoisted into constants.py):

   python3 -c "
   import sys
   for path in sys.argv[1:]:
       for ln, line in enumerate(open(path), 1):
           for c in line:
               cp = ord(c)
               if 0xE000 <= cp <= 0xF8FF or 0xF0000 <= cp <= 0xFFFFD:
                   print(f'{path}:{ln}  U+{cp:05X}  {c!r}')
   " claude/yas/*.py claude/yas/info/*.py claude/yas/render/*.py
   

   Any hit on a line you plan to Edit triggers the PUA refactor rule below.
3. Baseline tests: make test (or uv run pytest -q). Note pass count. On Android (Termux) uv run/make test is unavailable — activate the prebuilt venv and run pytest directly:

   . ~/.uvenv/bin/activate
   pytest -n 4 test/
   

4. Baseline demo: make demo (or make statusline/test, both run uv run python ops/demo.py). It animates 60 frames in place via cursor escapes; eyeball the final frame and the elbow alignment as it crosses layout thresholds (narrow → medium → wide on $COLUMNS). For static snapshot images, make demo/img (writes scenario PNGs into demo/, honours COLUMNS=). For a single piped frame when you need stdout, render one directly: COLUMNS=160 uv run python claude/statusline_command.py < ops/session-info-example.json (no transcript-derived rows; enough for border math). For a precise, diff-able baseline instead of eyeballing colour, capture the snapshots as ANSI-stripped text via the yas-demo-text skill: make demo/img && .claude/skills/yas-demo-text/scripts/demo-text.sh && cp -r demo/text /tmp/yas-base.

PUA refactor rule (mandatory before editing)

Nerd Font icons in this repo live in the Unicode Private Use Area (U+E000–U+F8FF and U+F0000–U+FFFFD). Literal PUA glyphs in source are invisible in many editors, render as □ in others, and get dropped through chat/agent round-trips — which makes Edit.old_string matching fail with a stale-looking "string to replace not found" error.

If a line you need to Edit contains a raw PUA glyph, hoist the glyph to a named constant in constants.py first, then Edit. No exceptions.

Convention (matches the existing block in constants.py):

# Nerd Font Private Use Area glyphs. Encoded as escapes so Edit, diff, and
# chat round-trips never lose the bytes. Render only in a Nerd-Font-capable
# terminal.
ICON_COST      = '\uefc8'     # nf-md currency-usd       (cost row)
ICON_TOK_RATE  = '\U000f18a7' # nf-md gauge              (t/m rate label)
GLYPH_MODEL    = '\U000f08b9' # nf-md monitor-dashboard  (model row)
GLYPH_THINKING = '\U000f1a53' # nf-md brain              (thinking indicator)

Import the constant where needed (from yas.constants import GLYPH_MODEL) and reference it in f-strings: f'{model_clr}{GLYPH_MODEL} {model_name}...'. Note that Renderer.ICON_PATH holds a colour code, not a glyph — don't reuse that namespace for glyphs. New glyph constants go in constants.py alongside ICON_COST/GLYPH_MODEL.

Runtime cost is zero — '\uefc8' (in source) and the literal glyph compile to the identical str object; CPython interns and the .pyc cache eliminates parse cost after first load.

Fallback when refactor isn't feasible mid-task

If the line has a PUA glyph and you genuinely can't refactor first (e.g., user is mid-edit and asked for one surgical change), use a Bash heredoc with python3 that reads, str.replaces, and writes. Python preserves the bytes exactly:

python3 << 'PY'
path = 'claude/yas/renderer.py'
with open(path) as f:
    s = f.read()
old = "...exact old text with raw glyph copied through Read...\n"
new = "...replacement...\n"
assert old in s, 'old not found'
with open(path, 'w') as f:
    f.write(s.replace(old, new, 1))
PY

This works because Read preserves the bytes when it loads them into your context, even when subsequent Edit calls can't transmit them through old_string.

Rendering invariants (silent-bug cheat-sheet)

These are the things pytest won't catch — get them wrong and the box draws crooked.

Width math

• Never use len() for column math. Use _visible_width (render/text.py) — it strips ANSI escapes via _ANSI_RE (constants.py) and counts wide chars (BMP emoji 0x1F300–0x1FAFF) as 2.
• Nerd Font PUA chars count as width 1. Correct in a Nerd-Font terminal; would be wrong elsewhere, but elsewhere isn't supported.

Column indexing on borders (render/borders.py)

• border_top(width, session_id='', downs=..., fill=..., pill=...), border_separator(width, ups=...), border_separator_dim(width, downs=..., ups=..., pill=..., pill_edge=...), border_bottom(width, ups=...) take 1-indexed visual positions of the inline │ they should attach an elbow to. Live on BorderRenderer; Renderer has matching delegators.
• border_line(content, width, fill=..., bg_lead='', bg_trail='', pill_flush=False, right_pill='') wraps content as │ <content>...│. Content starts at visual column 2, which is col-form 3 (1-indexed). right_pill paints a pill segment flush to the right edge.
• A Pill passed to border_top / border_separator_dim paints itself across [pill.start, pill.end] using border_char(col, edge) instead of the default top/separator glyph. pill_edge='top' is used when the pill sits below the separator.

vsep convention

The vertical divider inside a content row is the 5-char string ' │ ' (two spaces, pipe, two spaces). The │ sits at vsep-index 2.

vsep = f'  {self.BORDER}│{self.R}  '   # visible width 5; │ at offset 2

Section helpers that participate in dividers return (line, div_offset)

When a section contributes a │ that should grow elbows on the surrounding borders, the helper returns (line, div_offset) where div_offset is the 0-indexed visible position of the │ inside line. Examples: model_section_compact, model_right_section, tokens_cost (which returns (lines, vsep_cols, …)).

Caller (a build_* function) converts to a border col and threads it into RowSpec.downs / RowSpec.ups:

# Standalone row:
model_div_col = 3 + model_div_offset

# Inside a combined row whose own divider sits at top_div_col:
model_div_col = top_div_col + 3 + model_div_offset

rows = [
    RowSpec('top_border',     downs=(top_div_col, model_div_col)),
    RowSpec('content',        content=combined_line, bg_trail=bg_trail),
    RowSpec('separator_dim',  ups=(top_div_col, model_div_col)),
    ...
]

Every ┬ in a top border must line up with a │ in the row beneath it and a ┴ in the separator below — ups/downs are how you make that happen.

Gradient

grad_at(i, width, fill=...) returns the ANSI for column i of the rainbow border. Don't reorder the parts list when extending border helpers — the gradient is positional.

Layout-spec rules (layout.py)

• A build_* function returns a fully-populated LayoutSpec. Don't push rendering side effects into it; only build RowSpecs.
• New row types need: a new kind string, a branch in render_layout, and a BorderRenderer method (if it draws a border) or a Renderer section helper (if it's content).
• Conditional rows: append to a local rows: list[RowSpec] and assign spec.rows = rows at the end. See build_wide for the canonical pattern with optional plugins_line, task_row, and openspec_bars.
• When a row drops out (e.g., no plugins), the surrounding ups/downs need to be re-threaded — build_wide carries a next_ups/pending_ups local and a sep_kind helper for this. Don't try to "fix it up" inside render_layout.
• Pill threading: when the pill is active, the row immediately under the top border uses pill_flush=True and an empty bg_lead; the surrounding top_border / separator_dim receive the same Pill object. When the pill is inactive, you fall back to bg_lead/bg_trail and elbow ups/downs.

Post-edit checklist

1. make test (uv run pytest -q; on Android (Termux) use . ~/.uvenv/bin/activate && pytest -n 4 test/) — must be green. The pass count should match the baseline plus any tests you added.
2. make demo — eyeball the animation:
   • Every ┬ in a top border lines up with a │ in the row beneath it and a ┴ in the separator below.
   • Pill colours flow continuously across the top, sides, and bottom of the model row.
   • Resize the terminal narrower/wider during the run to verify the narrow ↔ medium ↔ wide thresholds.
   • For an exact comparison, re-strip and diff against the baseline from the pre-edit step: make demo/img && .claude/skills/yas-demo-text/scripts/demo-text.sh && diff -ru /tmp/yas-base demo/text. Every moved cell shows up as a line diff — this catches off-by-one column bugs the eye misses across the 60-frame animation.
3. Tests — any behaviour change needs a test added or updated. Tests resolve the package via pythonpath = ["claude"] and import modules as yas.<module> / yas.info.<module> / yas.render.<module>; conftest.py exposes a strip_ansi fixture (from test/helper.py) and a tmp_home fixture that patches CLAUDE_DIR across yas.app/yas.config/yas.constants/yas.session/yas.info.subagents/yas.tokens. Width-sensitive assertions go through _visible_width. Put new tests in the file that matches the layer touched: test_gradient_math.py, test_borders.py, test_model_section.py, test_context_line.py, test_openspec_bar.py, test_tokens_cost.py, test_config.py, test_layout_seam.py, test_subagent_rows.py/test_subagent_metrics.py/test_cohort_visibility.py (subagents), test_info.py (denominator math, _fmt_elapsed, laziness), etc. Layout tests inject a SessionView directly — construct one with a known SessionInfo and Config rather than calling the builders with raw reader data.
4. CONTEXT.md — if any displayed term changed (label, glyph meaning, what a number represents), update the glossary in the same change.

Multi-session observer (claude/mon.py/claude/mon/) module map is in ARCHITECTURE.md. Launch it with make mon/run.

Sibling skills

python-style applies as usual when touching .py files. This skill adds the statusline-specific rules on top. After a render change, use yas-demo-text to turn make demo/img snapshots into ANSI-stripped plain text for a before/after diff (see the demo steps above) — the reliable way to confirm column math instead of eyeballing the coloured animation.