Playback Mode Pages

TECHNICAL_GUIDE.md

@@ -167,9 +167,11 @@ The existing recordings contain one bar of count-in, 168 main-form bars, three h
 
 Score timing includes `sustain_start`, an exact measure boundary, as well as the total written duration. Ending measures carry `ending_sustain`; Python and C++ validate a contiguous tail and consistent timing. Older scores without the new timing field retain their previous full-duration click behavior. Both toggles play the recorded count-in alone, then backing plus sample clicks until `sustain_start`. No clicks sound over the ending. Metronome-only supplies its own count-in and completes after the three silent held bars. Backing-only plays the complete file and decay. Both off enables manual navigation; hold exits and natural completion returns to the part menu. The final page remains visible through decay.
 
-Preparation runs on a worker: checksums and samples are loaded before publishing a Sonus recording transport. Sonus streams backing audio through miniaudio’s background resource manager and mixes preloaded stereo clicks on the same rendered-frame clock. Callback work uses preallocated buffers, and resource retirement occurs on control threads. Stream failures stop progress and surface an error. Absolute rational beat positions are rounded to frames at 48 kHz once per position, avoiding accumulated rounding drift. The UI polls that audio clock for page boundaries and Count-in/Playing/Sustain status; wall-clock timers never determine musical progress.
+Preparation runs on a worker: checksums and samples are loaded before publishing a Sonus recording transport. Sonus streams backing audio through miniaudio’s background resource manager and mixes preloaded stereo clicks on the same rendered-frame clock. Callback work uses preallocated buffers, and resource retirement occurs on control threads. Stream failures stop progress and surface an error. Absolute rational beat positions are rounded to frames at 48 kHz once per position, avoiding accumulated rounding drift. The UI polls that audio clock for system and measure boundaries and Count-in/Playing/Sustain status; wall-clock timers never determine musical progress.
 
-Page metadata comes from actual system pagination and is preserved and revalidated in engraving caches. The UI prepares the current and next page before playback starts and retains a two-texture cache. Session and catalog identities reject stale preparation, page updates and completion after cancellation. Missing or corrupt pages/audio leave a visible error and permit hold/back. `--once` validates packaged recording checksums and all score pages without opening audio/display hardware.
+Page metadata comes from actual system pagination and is preserved and revalidated in engraving caches. `presentation.pages` partitions the music into normal two-system pages. `presentation.playback_pages` holds one view per system: that system and its successor, or a final single top system. Both reuse the same system breaks, horizontal geometry, and part-wide scale, fitted against every adjacent pair. Each descriptor carries system measure ranges, exact beat boundaries, and page-coordinate rectangles for its measure labels. Normal systems partition the score; overlapping playback views must match that canonical partition. Bundles missing playback metadata require regeneration.
+
+Measure numbers are centered over their starting barlines (the staff’s left edge at system start), in a reserved lane above notation and below harmony/section labels. The display outlines the current label using the page texture’s letterbox transform; count-in, preparation, exit, and playback error clear it. Measure updates publish even when the line stays unchanged. Normal catalog page counts remain unchanged; the loader reads the separate playback count from bundle metadata. During automatic playback, navigation bounds, the header’s Line counter, and Pico’s page/pages fields refer to overlapping views. Manual browsing uses the normal sequence. The UI prepares the current and next page before playback starts and retains a two-texture cache. Session and catalog identities reject stale preparation, page updates and completion after cancellation. Missing or corrupt pages/audio leave a visible error and permit hold/back. `--once` validates packaged recording checksums and both normal and playback score pages without opening audio/display hardware.
 
 ### Authored Repertoire and Learned Solos
 
@@ -263,7 +265,7 @@ Voices retain separate stems and collision offsets; chord tones retain their own
 
 Generated guitar tones carry `tablature: {string, fret}`; their staff is marked `tablature: true`. `engraving/tablature.py` draws a six-line TAB view below standard notation, sharing onset columns, barlines, and page breaks. Both views belong to one system and never duplicate the semantic timeline or playback events. Standard notation carries rhythm, rests, and tuplets; TAB carries positions, solo slashes, and tied continuations without rest glyphs. Strings and frets are validated against sounding pitch, and the layout audit checks each visible TAB numeral's position and alignment.
 
-Every part uses two music systems per page; only an odd final system occupies a row alone. A compact title/composer/part header reserves the same height on every page, wrapping credits if necessary. Pagination fits the two systems using their individual heights and distributes extra whitespace around them while retaining minimum system and header/footer clearances. One uniform scale applies throughout the entire part, reducing the ordinary notation size only when required by the tallest pair. Notation, TAB, text, and anchors scale together without changing musical content. Guitar layout starts with 10-pixel notation spacing, 10.5-pixel TAB spacing, 12-pixel fret labels, and a 14-pixel minimum gap between systems. The unscaled TAB spacing accommodates Petaluma numerals up to 9.75 pixels tall. Tempo markings consume neither ink nor spacing; their semantic data is preserved. Existing `.pages/*.png` preview files are the exact packaged page textures.
+Normal pages use two music systems; only an odd final system occupies a row alone. Playback pages use overlapping adjacent pairs and always finish with the last system alone on top. A compact title/composer/part header reserves the same height on every page, wrapping credits if necessary. Pagination fits the two systems using their individual heights and distributes extra whitespace around them while retaining minimum system and header/footer clearances. One uniform scale applies throughout the entire part, reducing the ordinary notation size only when required by the tallest adjacent pair, including transition pages. Notation, TAB, text, and anchors scale together without changing musical content. Guitar layout starts with 10-pixel notation spacing, 10.5-pixel TAB spacing, 12-pixel fret labels, and a 14-pixel minimum gap between systems. The unscaled TAB spacing accommodates Petaluma numerals up to 9.75 pixels tall. Tempo markings consume neither ink nor spacing; their semantic data is preserved. Existing `.pages/*.png` preview files are the exact packaged page textures.
 
 Line breaks occur only at measure boundaries. Each line fits as many complete measures as readable spacing allows; it never fills remaining space with a partial measure. A complete measure exceeding the available width or height fails with source and measure context instead of being split or squeezed to fit. Authored ties, beams, tuplets, and lyric spans can continue across whole-measure line breaks. Column measurement and fit trials reuse a score index and bounded column cache. Page placement then re-spaces columns for the final height-fitting scale, keeping every notation/TAB staff at the same physical left and right margins without stretching glyphs. Non-final lines are justified; a short final line retains natural note spacing while staff lines extend to the same right margin. Layout audits enforce these margins as well as musical coverage.