feat(bank_panel): docked bank grid with LICE waveform thumbnails (M5 Wave A)

Docked SWELL window toggled by a new action, drawing the current bank as
per-sample min/max thumbnails (PCM_source + peaks) with an in-memory cache.
Pure grid-layout/cache-key math in bank_grid (tested). Renames peaks::Sample
-> AudioSample to avoid colliding with bank_model::Sample.

CMakeLists.txt

@@ -36,6 +36,15 @@ target_include_directories(peaks PUBLIC src)
 add_library(capture_paths STATIC src/capture_paths.cpp)
 target_include_directories(capture_paths PUBLIC src)
 
+# ---------------------------------------------------------------------------
+# 2c) Pure bank-grid layout — NO REAPER, NO SWELL. Grid tiling math (panel WxH +
+#     cell size + N -> cell rects, wrapping, partial last row) and the thumbnail
+#     cache key for the docked bank_panel (M5). Split out so the layout logic is
+#     unit-tested outside the DAW; the panel shell (SWELL/LICE/PCM) is DAW-verified.
+# ---------------------------------------------------------------------------
+add_library(bank_grid STATIC src/bank_grid.cpp)
+target_include_directories(bank_grid PUBLIC src)
+
 # ---------------------------------------------------------------------------
 # 3) Standalone tests for the pure modules (run without launching REAPER).
 # ---------------------------------------------------------------------------
@@ -52,21 +61,39 @@ add_executable(capture_paths_tests tests/test_capture_paths.cpp)
 target_link_libraries(capture_paths_tests PRIVATE capture_paths)
 add_test(NAME capture_paths_tests COMMAND capture_paths_tests)
 
+add_executable(bank_grid_tests tests/test_bank_grid.cpp)
+target_link_libraries(bank_grid_tests PRIVATE bank_grid)
+add_test(NAME bank_grid_tests COMMAND bank_grid_tests)
+
 # ---------------------------------------------------------------------------
 # 4) The REAPER extension — a loadable module (dlopen'd by REAPER, not linked).
 # ---------------------------------------------------------------------------
+# LICE sources the bank_panel draws with: lice.cpp (LICE_SysBitmap, FillRect,
+# Clear, Blit) + lice_line.cpp (Line, DrawRect). lice_line.cpp's bezier helpers
+# call LICE_FillCircle from lice_arc.cpp, so that TU is required to link even
+# though the panel draws no arcs. LICE routes GDI through native Win32 or, on
+# mac/linux, the host SWELL (SWELL_PROVIDED_BY_APP).
+set(LICE_SRC
+    ${WDL_INC}/lice/lice.cpp
+    ${WDL_INC}/lice/lice_line.cpp
+    ${WDL_INC}/lice/lice_arc.cpp
+)
+
 add_library(reaper_reasampler MODULE
     src/main.cpp
     src/capture.cpp
     src/persist.cpp
+    src/bank_panel.cpp
+    ${LICE_SRC}
 )
-target_link_libraries(reaper_reasampler PRIVATE bank_model capture_paths)
+target_link_libraries(reaper_reasampler PRIVATE bank_model capture_paths peaks bank_grid)
 target_include_directories(reaper_reasampler PRIVATE ${SDK_INC} ${WDL_INC})
 set_target_properties(reaper_reasampler PROPERTIES PREFIX "" OUTPUT_NAME "reaper_reasampler")
 
 if(WIN32)
-    # Native Win32. REAPER provides nothing extra to link.
-    # Dialog resources return with the docked bank_panel (Milestone 5).
+    # Native Win32. REAPER provides nothing extra to link. The bank_panel dialog
+    # template (M5) is compiled from src/resource.rc by the platform RC compiler.
+    target_sources(reaper_reasampler PRIVATE src/resource.rc)
 
 elseif(APPLE)
     # macOS: use REAPER's OWN SWELL at runtime via the modstub.
@@ -75,7 +102,10 @@ elseif(APPLE)
     target_compile_definitions(reaper_reasampler PRIVATE SWELL_PROVIDED_BY_APP)
     target_link_libraries(reaper_reasampler PRIVATE "-framework AppKit")
     set_target_properties(reaper_reasampler PROPERTIES SUFFIX ".dylib")
-    # Dialog: run SWELL resgen once (see README) and add the generated source.
+    # bank_panel dialog (M5): SWELL can't read a Win32 .rc directly. Run resgen
+    # once to turn src/resource.rc into a C++ source, then add it here:
+    #   php ${WDL_INC}/swell/mac_resgen.php src/resource.rc
+    # target_sources(reaper_reasampler PRIVATE src/resource.rc_mac_dlg.h)  # generated
 
 else()
     # Linux: REAPER's libSwell.so is used at runtime via the generic modstub.
@@ -83,5 +113,8 @@ else()
     target_sources(reaper_reasampler PRIVATE ${SWELL}/swell-modstub-generic.cpp)
     target_compile_definitions(reaper_reasampler PRIVATE SWELL_PROVIDED_BY_APP)
     set_target_properties(reaper_reasampler PROPERTIES SUFFIX ".so")
-    # Dialog: run SWELL resgen once (see README) and add the generated source.
+    # bank_panel dialog (M5): reuse the macOS resgen output (see README /
+    # CLAUDE.md §SWELL dialog resources), then add the generated source:
+    #   php ${WDL_INC}/swell/mac_resgen.php src/resource.rc
+    # target_sources(reaper_reasampler PRIVATE src/resource.rc_mac_dlg.h)  # generated
 endif()

src/bank_grid.cpp

@@ -0,0 +1,65 @@
+// bank_grid — pure implementation. See bank_grid.h. NO REAPER / SWELL / vendor.
+
+#include "bank_grid.h"
+
+namespace reasampler {
+
+int columnsForWidth(int panelWidth, const GridSpec& spec) {
+    // Layout: [gap][cell][gap][cell]...[cell][gap]. n cells occupy
+    // gap + n*(cellWidth + gap). Solve for the largest n that fits panelWidth,
+    // clamped to at least 1 so a too-narrow panel still shows a (clipped) column.
+    const int cell = spec.cellWidth + spec.gap;
+    if (cell <= 0) return 1;  // degenerate spec — one column, avoid divide-by-zero
+    const int usable = panelWidth - spec.gap;
+    if (usable < spec.cellWidth) return 1;
+    const int cols = usable / cell;
+    return cols < 1 ? 1 : cols;
+}
+
+std::vector<CellRect> computeCellRects(int itemCount,
+                                       int panelWidth,
+                                       const GridSpec& spec) {
+    std::vector<CellRect> rects;
+    if (itemCount <= 0) return rects;
+
+    const int cols = columnsForWidth(panelWidth, spec);
+    rects.reserve(static_cast<std::size_t>(itemCount));
+
+    for (int i = 0; i < itemCount; ++i) {
+        const int col = i % cols;
+        const int row = i / cols;
+        CellRect r;
+        r.x = spec.gap + col * (spec.cellWidth + spec.gap);
+        r.y = spec.gap + row * (spec.cellHeight + spec.gap);
+        r.width = spec.cellWidth;
+        r.height = spec.cellHeight;
+        rects.push_back(r);
+    }
+    return rects;
+}
+
+int contentHeight(int itemCount, int panelWidth, const GridSpec& spec) {
+    if (itemCount <= 0) return 0;
+    const int cols = columnsForWidth(panelWidth, spec);
+    // Ceil-divide item count by columns to get the row count (partial last row
+    // still occupies a full row of height).
+    const int rows = (itemCount + cols - 1) / cols;
+    return spec.gap + rows * (spec.cellHeight + spec.gap);
+}
+
+std::string thumbnailKeyString(const ThumbnailKey& key) {
+    // Length-prefix the sampleId so a delimiter byte inside an id cannot forge a
+    // collision with a different (id, width, generation) triple.
+    std::string s;
+    s.reserve(key.sampleId.size() + 32);
+    s += std::to_string(key.sampleId.size());
+    s += ':';
+    s += key.sampleId;
+    s += '|';
+    s += std::to_string(key.width);
+    s += '|';
+    s += std::to_string(key.generation);
+    return s;
+}
+
+} // namespace reasampler

src/bank_grid.h

@@ -0,0 +1,88 @@
+#pragma once
+// bank_grid — the REAPER-free layout math and cache-key logic behind the docked
+// bank_panel (M5, Wave A). The panel shell (bank_panel.cpp) owns the SWELL window,
+// LICE drawing, and PCM reads; ALL of that is REAPER-bound and DAW-verified. What
+// is NOT DAW-bound — how N sample cells tile a panel of a given pixel size, and
+// the key that identifies a cached thumbnail — lives here so it is unit-tested
+// outside the DAW (CLAUDE.md §load-bearing split).
+//
+// PURE MODULE: NO REAPER types, NO SWELL, NO vendor/ includes. Standard library
+// only. Builds and unit-tests without REAPER.
+
+#include <cstddef>
+#include <cstdint>
+#include <string>
+#include <vector>
+
+namespace reasampler {
+
+// A single cell's pixel rectangle within the panel, top-left origin (SWELL/LICE
+// convention). (x, y) is the top-left corner; width/height are the cell extents.
+// These are the draw bounds for one sample's thumbnail; the panel draws its
+// waveform envelope inside this rect (minus any internal padding it applies).
+struct CellRect {
+    int x = 0;
+    int y = 0;
+    int width = 0;
+    int height = 0;
+
+    bool operator==(const CellRect& o) const {
+        return x == o.x && y == o.y && width == o.width && height == o.height;
+    }
+};
+
+// Fixed inputs that shape the grid. All in pixels. cellWidth/cellHeight are the
+// TARGET cell size; the layout fits as many whole columns as the panel width
+// allows (>= 1) and wraps to as many rows as N requires. gap is the pixel spacing
+// between adjacent cells (and the outer margin), so cells never touch.
+struct GridSpec {
+    int cellWidth = 120;
+    int cellHeight = 72;
+    int gap = 8;
+};
+
+// Computes the number of columns that fit in a panel of the given pixel width for
+// the spec. Always >= 1 (a panel narrower than one cell still shows one column,
+// clipped by the window). Pure arithmetic — the panel passes its live client
+// width here and to computeCellRects.
+int columnsForWidth(int panelWidth, const GridSpec& spec);
+
+// Tiles `itemCount` cells left-to-right, top-to-bottom into a panel of the given
+// pixel width, honoring the spec's cell size and gap. Returns exactly itemCount
+// rects in item order (rect i is sample i). A partial last row is left-aligned
+// and simply shorter — no centering, no stretching. itemCount == 0 -> empty.
+// panelWidth is used only to derive the column count; the returned rects may
+// extend below any fixed viewport height (the panel scrolls/clips in Wave B).
+std::vector<CellRect> computeCellRects(int itemCount,
+                                       int panelWidth,
+                                       const GridSpec& spec);
+
+// The total pixel height the grid occupies for itemCount cells at the given panel
+// width and spec (top margin + rows*cellHeight + inter-row gaps + bottom margin).
+// 0 when itemCount == 0. The panel uses this to know its full content height
+// (scroll extent in Wave B; for Wave A it sizes the empty-vs-populated decision).
+int contentHeight(int itemCount, int panelWidth, const GridSpec& spec);
+
+// Identifies one cached thumbnail. A cached envelope is valid only while the
+// sample's identity, the draw width it was computed at, and the bank generation
+// it was computed under all match. Width is part of the key because the envelope
+// has exactly `width` bins per channel (peaks::computeEnvelope is width-driven);
+// a resized panel needs a fresh envelope. Generation lets the panel invalidate
+// every entry when the bank changes (capture / project load) without diffing.
+struct ThumbnailKey {
+    std::string sampleId;
+    int width = 0;
+    std::uint64_t generation = 0;
+
+    bool operator==(const ThumbnailKey& o) const {
+        return sampleId == o.sampleId && width == o.width &&
+               generation == o.generation;
+    }
+};
+
+// A stable string form of the key, suitable as a map key. Deterministic: the same
+// key always yields the same string, distinct keys always differ (the sampleId is
+// length-prefixed so an id containing the delimiter cannot collide with another).
+std::string thumbnailKeyString(const ThumbnailKey& key);
+
+} // namespace reasampler

src/bank_panel.cpp

@@ -0,0 +1,446 @@
+// bank_panel.cpp — REAPER-facing docked grid (M5, Wave A). See bank_panel.h.
+//
+// Compiled into the reaper_reasampler MODULE. Includes reaper_plugin_functions.h
+// WITHOUT REAPERAPI_IMPLEMENT — main.cpp owns the API pointers; here they are
+// extern (CLAUDE.md §contract).
+//
+// What this file owns (all REAPER/SWELL/LICE-bound, hence DAW-verified, not unit
+// tested):
+//   * a SWELL dialog (IDD_BANK_PANEL) docked via DockWindowAddEx / undocked via
+//     DockWindowRemove; toggled open/closed.
+//   * WM_PAINT: draw the current bank as a grid of waveform thumbnails using LICE,
+//     or a centered empty-state string when the bank is empty.
+//   * per-sample PCM read via PCM_source (PCM_Source_CreateFromFile +
+//     PCM_source::GetSamples) fed to peaks::computeEnvelope at the cell width.
+//   * an in-memory thumbnail cache keyed by (sample id, draw width, bank
+//     generation) so paint does not recompute envelopes every frame.
+//
+// READ-ONLY (load-bearing principle): this panel never inserts into the arrange
+// and never mutates the project or the bank. It only reads g_session.bank() and
+// reads sample files off disk.
+//
+// THUMBNAIL-CACHE DECISION (CONTEXT.md §Open questions "recompute vs store peak
+// bins alongside the index"): for Wave A we RECOMPUTE into an in-memory cache and
+// do NOT persist peak bins in the index. Rationale: the persisted index stays
+// lean and format-stable; envelopes are cheap to recompute on demand and must be
+// recomputed anyway whenever the panel width (bin count) changes, which a stored
+// fixed-resolution bin set could not satisfy. Storing bins is a later optimization
+// if profiling shows recompute cost matters (it is bounded: one read + one O(frames)
+// pass per sample, only on cache miss).
+
+#include "bank_panel.h"
+
+#include <cstdint>
+#include <filesystem>
+#include <string>
+#include <unordered_map>
+#include <vector>
+
+#include "bank_grid.h"
+#include "bank_model.h"
+#include "capture_paths.h"
+#include "peaks.h"
+#include "persist.h"
+
+// SWELL / LICE. On macOS/Linux SWELL is provided by the host (SWELL_PROVIDED_BY_APP);
+// on Windows we use native Win32 (windows.h first, then swell.h no-ops on _WIN32).
+// LICE routes its GDI through whichever backend is active. wdltypes.h gives
+// WDL_DLGRET (the platform dialog-proc return type).
+#ifdef _WIN32
+#include <windows.h>
+#endif
+#include "wdltypes.h"
+#include "swell/swell.h"
+#include "lice/lice.h"
+
+#include "resource.h"
+
+#define REAPERAPI_MINIMAL
+#define REAPERAPI_WANT_DockWindowAddEx
+#define REAPERAPI_WANT_DockWindowActivate
+#define REAPERAPI_WANT_DockWindowRemove
+#define REAPERAPI_WANT_EnumProjects
+#define REAPERAPI_WANT_GetMainHwnd
+#define REAPERAPI_WANT_PCM_Source_CreateFromFile
+#define REAPERAPI_WANT_PCM_Source_Destroy
+#include "reaper_plugin_functions.h"
+
+// main.cpp owns the module instance handle (needed to load the dialog resource).
+extern REAPER_PLUGIN_HINSTANCE g_hInst;
+
+namespace reasampler {
+
+namespace {
+
+namespace fs = std::filesystem;
+
+// --- Layout / palette constants (Wave A: fixed, no user config — YAGNI) -------
+
+// Cell size + spacing for the grid. Tuned for a legible thumbnail at a glance;
+// revisit when audition/selection UI lands (Wave B) and cells gain chrome.
+const GridSpec kGrid{/*cellWidth=*/140, /*cellHeight=*/84, /*gap=*/10};
+
+// How many PCM frames to pull per sample for the thumbnail. The envelope is drawn
+// at cell width (~140 bins), so a few thousand frames per bin is ample; capping
+// the read keeps a long sample's thumbnail cheap without a streaming loop. A
+// captured one-shot/loop is short; a full-mix bounce is downsampled visually
+// anyway. If a sample is longer than this, the thumbnail shows its head — an
+// acceptable Wave-A approximation, flagged for Wave B (whole-file overview).
+constexpr int kMaxThumbnailFrames = 1 << 20;  // ~1M frames (~22s @ 48k)
+
+const LICE_pixel kColBackground = LICE_RGBA(28, 28, 30, 255);
+const LICE_pixel kColCellBg      = LICE_RGBA(44, 44, 48, 255);
+const LICE_pixel kColCellBorder  = LICE_RGBA(70, 70, 76, 255);
+const LICE_pixel kColWaveform    = LICE_RGBA(120, 200, 160, 255);
+const LICE_pixel kColMidline     = LICE_RGBA(60, 60, 66, 255);
+const LICE_pixel kColText        = LICE_RGBA(200, 200, 205, 255);
+
+// --- Panel state --------------------------------------------------------------
+
+// A computed thumbnail: the per-channel envelope at a known width. Held in the
+// cache so paint reuses it until the sample, width, or bank generation changes.
+struct CachedThumbnail {
+    Envelope envelope;   // one ChannelEnvelope per channel, `width` bins each
+    int width = 0;       // bins per channel this envelope was computed at
+};
+
+struct PanelState {
+    ReaSamplerSession* session = nullptr;
+
+    HWND hwnd = nullptr;         // the docked dialog, null when closed
+    bool open = false;
+
+    // Bank-change detection: a cheap fingerprint of the bank (count + ids +
+    // relative paths). When it changes we bump `generation`, which invalidates
+    // every cache entry (keyed by generation) and forces a repaint. Simpler than
+    // adding a mutation counter to BankIndex, and correct across same-count
+    // project-load swaps (the fingerprint includes ids/paths, not just size).
+    std::string bankFingerprint;
+    std::uint64_t generation = 0;
+
+    // Thumbnail cache: key string (bank_grid::thumbnailKeyString) -> envelope.
+    // Entries for stale generations are lazily overwritten on next miss; a bank
+    // change also clears it wholesale (see refreshFingerprint) to bound memory.
+    std::unordered_map<std::string, CachedThumbnail> cache;
+};
+
+PanelState g_panel;
+
+// --- Current-project directory (mirrors persist.cpp's derivation) -------------
+//
+// The index stores relative paths; resolving a bank file needs the current .rpp
+// directory. persist.cpp derives this the same way for load; the panel is its own
+// shell so it reads it directly rather than threading state through the session.
+// FOLLOW-UP: capture.cpp, persist.cpp, and now bank_panel.cpp each carry this
+// two-line derivation — a shared REAPER helper ("current project dir") is a clean
+// small refactor once a third consumer exists (now it does). Out of scope this wave.
+std::string currentProjectDir() {
+    std::vector<char> buf(4096, '\0');
+    EnumProjects(-1, buf.data(), static_cast<int>(buf.size()));
+    std::string rpp(buf.data());
+    if (rpp.empty()) return {};  // unsaved project: no resolvable bank
+    return normalizeSlashes(fs::path(rpp).parent_path().string());
+}
+
+// --- Thumbnail computation ----------------------------------------------------
+
+// Reads up to kMaxThumbnailFrames of interleaved PCM from `absPath` and computes a
+// per-channel min/max envelope at `width` bins. Returns an empty envelope on any
+// failure (missing file, unreadable source, zero-length) — the caller draws an
+// empty cell rather than propagating an error. READ-ONLY: opens the file through
+// a PCM_source and destroys it; never touches the project.
+Envelope computeThumbnail(const std::string& absPath, int width) {
+    if (width <= 0 || absPath.empty()) return {};
+
+    PCM_source* src = PCM_Source_CreateFromFile(absPath.c_str());
+    if (!src) return {};
+
+    const int nch = src->GetNumChannels();
+    const double srate = src->GetSampleRate();
+    const double lengthSec = src->GetLength();
+    if (nch <= 0 || srate < 1.0 || lengthSec <= 0.0) {
+        PCM_Source_Destroy(src);
+        return {};
+    }
+
+    // Frames to read: the whole sample, capped so a long bounce stays cheap.
+    std::int64_t totalFrames = static_cast<std::int64_t>(lengthSec * srate);
+    if (totalFrames <= 0) { PCM_Source_Destroy(src); return {}; }
+    int frames = totalFrames > kMaxThumbnailFrames
+                     ? kMaxThumbnailFrames
+                     : static_cast<int>(totalFrames);
+
+    // One GetSamples call filling a caller-allocated interleaved buffer. block.length
+    // is the requested frame count; samples_out reports what was actually rendered
+    // (may be short at end-of-file). We ask at the source's own rate so no resample.
+    std::vector<ReaSample> buf(static_cast<std::size_t>(frames) * nch, 0.0);
+    PCM_source_transfer_t block{};
+    block.time_s = 0.0;
+    block.samplerate = srate;
+    block.nch = nch;
+    block.length = frames;
+    block.samples = buf.data();
+    block.samples_out = 0;
+    src->GetSamples(&block);
+
+    PCM_Source_Destroy(src);
+
+    const int got = block.samples_out;
+    if (got <= 0) return {};
+
+    // ReaSample is double in some builds, float in others; peaks consumes float
+    // (peaks::Sample is a float alias, its native buffer type). Convert at this
+    // boundary — use `float` explicitly, NOT `reasampler::Sample`, because that
+    // name also denotes bank_model's metadata struct in this same namespace when
+    // both headers are visible (they are here in the module).
+    const std::size_t sampleCount = static_cast<std::size_t>(got) * nch;
+    std::vector<float> pcm(sampleCount);
+    for (std::size_t i = 0; i < sampleCount; ++i)
+        pcm[i] = static_cast<float>(buf[i]);
+
+    return computeEnvelope(pcm, static_cast<std::size_t>(nch),
+                           static_cast<std::size_t>(got),
+                           static_cast<std::size_t>(width));
+}
+
+// Returns the cached envelope for `sample` at `width`, computing+inserting it on a
+// miss. Keyed by (id, width, current generation) so a resize or bank change misses
+// and recomputes. `projectDir` resolves the sample's relative path to disk.
+const Envelope& thumbnailFor(const Sample& sample, int width,
+                             const std::string& projectDir) {
+    ThumbnailKey key{sample.id, width, g_panel.generation};
+    const std::string ks = thumbnailKeyString(key);
+
+    auto it = g_panel.cache.find(ks);
+    if (it != g_panel.cache.end()) return it->second.envelope;
+
+    const std::string abs = resolveBankFile(projectDir, sample.relativePath);
+    CachedThumbnail thumb;
+    thumb.width = width;
+    thumb.envelope = computeThumbnail(abs, width);
+    auto ins = g_panel.cache.emplace(ks, std::move(thumb));
+    return ins.first->second.envelope;
+}
+
+// --- Drawing ------------------------------------------------------------------
+
+// Draws one sample's envelope into `rect` of `bmp`: a cell background, border, a
+// zero midline, and the min/max waveform. Multi-channel envelopes are stacked
+// vertically (each channel gets an equal horizontal band) so a stereo sample shows
+// both channels without folding (precision invariant: no stereo fold).
+void drawThumbnail(LICE_IBitmap* bmp, const CellRect& rect, const Envelope& env) {
+    LICE_FillRect(bmp, rect.x, rect.y, rect.width, rect.height, kColCellBg, 1.0f, 0);
+    LICE_DrawRect(bmp, rect.x, rect.y, rect.width, rect.height, kColCellBorder, 1.0f, 0);
+
+    if (env.empty()) {
+        // Unreadable / empty sample: cell drawn, no waveform. A single midline
+        // signals "cell present, no data" without an error dialog.
+        const int midY = rect.y + rect.height / 2;
+        LICE_Line(bmp, rect.x + 2, midY, rect.x + rect.width - 2, midY,
+                  kColMidline, 1.0f, 0, false);
+        return;
+    }
+
+    const int channels = static_cast<int>(env.size());
+    const int bandH = rect.height / channels;
+
+    for (int ch = 0; ch < channels; ++ch) {
+        const ChannelEnvelope& bins = env[ch];
+        const int bandTop = rect.y + ch * bandH;
+        const int midY = bandTop + bandH / 2;
+        // half-height in pixels a full-scale (|value|==1) sample reaches, minus a
+        // 2px inset so the waveform never touches the cell border.
+        const double halfSpan = (bandH / 2) - 2;
+
+        LICE_Line(bmp, rect.x + 2, midY, rect.x + rect.width - 2, midY,
+                  kColMidline, 1.0f, 0, false);
+
+        const int nbins = static_cast<int>(bins.size());
+        if (nbins <= 0) continue;
+
+        // Map bin i -> a column x within the cell's inner width. The envelope was
+        // computed at `width` bins == the cell's drawable columns, so bin i maps
+        // to column i; guard anyway if they differ (e.g. cached at another width).
+        const int innerW = rect.width - 4;  // 2px inset each side
+        for (int i = 0; i < nbins; ++i) {
+            const int x = rect.x + 2 + (nbins > 1 ? (i * (innerW - 1)) / (nbins - 1) : 0);
+            // min<=max always (peaks invariant). Draw a vertical line from the
+            // min sample to the max sample, clamped to the band.
+            int yMax = midY - static_cast<int>(bins[i].max * halfSpan);  // max -> up
+            int yMin = midY - static_cast<int>(bins[i].min * halfSpan);  // min -> down
+            if (yMax < bandTop) yMax = bandTop;
+            if (yMin > bandTop + bandH - 1) yMin = bandTop + bandH - 1;
+            LICE_Line(bmp, x, yMin, x, yMax, kColWaveform, 1.0f, 0, false);
+        }
+    }
+}
+
+// Draws the empty-state message centered in the client area.
+void drawEmptyState(HWND hwnd, LICE_IBitmap* bmp, int w, int h) {
+    (void)hwnd;
+    LICE_Clear(bmp, kColBackground);
+    HDC dc = bmp->getDC();
+    if (!dc) return;
+    const char* msg = "No samples in this project's bank yet. Capture one to see it here.";
+    RECT rc{0, 0, w, h};
+    SetTextColor(dc, RGB(200, 200, 205));
+    SetBkMode(dc, TRANSPARENT);
+    DrawText(dc, msg, -1, &rc, DT_CENTER | DT_VCENTER | DT_SINGLELINE | DT_WORDBREAK);
+}
+
+// The full paint: build/refresh the LICE backing bitmap at client size, draw the
+// grid (or empty state), then blit to the window HDC.
+void paintPanel(HWND hwnd, HDC hdc) {
+    RECT cr{};
+    GetClientRect(hwnd, &cr);
+    const int w = cr.right - cr.left;
+    const int h = cr.bottom - cr.top;
+    if (w <= 0 || h <= 0) return;
+
+    // A per-paint sysbitmap. Cheap to construct; sized to the client. (Wave A
+    // keeps it local; if repaint cost ever matters, cache it across paints.)
+    LICE_SysBitmap bmp(w, h);
+
+    const BankIndex* bank = g_panel.session ? &g_panel.session->bank() : nullptr;
+    if (!bank || bank->empty()) {
+        drawEmptyState(hwnd, &bmp, w, h);
+    } else {
+        LICE_Clear(&bmp, kColBackground);
+        const std::string projectDir = currentProjectDir();
+        const std::vector<Sample>& samples = bank->all();
+        const std::vector<CellRect> rects =
+            computeCellRects(static_cast<int>(samples.size()), w, kGrid);
+        // Draw each cell's thumbnail. Inner drawable width == cell width - inset;
+        // compute the envelope at the cell's inner column count so bins map 1:1.
+        const int binWidth = kGrid.cellWidth - 4;
+        for (std::size_t i = 0; i < rects.size(); ++i) {
+            const CellRect& rect = rects[i];
+            // Skip cells entirely below the viewport (Wave A has no scroll; this
+            // just avoids computing thumbnails that cannot be seen).
+            if (rect.y >= h) continue;
+            const Envelope& env = thumbnailFor(samples[i], binWidth, projectDir);
+            drawThumbnail(&bmp, rect, env);
+        }
+    }
+
+    BitBlt(hdc, 0, 0, w, h, bmp.getDC(), 0, 0, SRCCOPY);
+}
+
+// --- Bank-change detection ----------------------------------------------------
+
+// A cheap fingerprint of the bank: count + each sample's id and relative path.
+// Ids are unique and stable; including relative paths catches an in-place file
+// swap. Cheaper than hashing PCM, sufficient to know "the grid must redraw".
+std::string bankFingerprint(const BankIndex& bank) {
+    std::string fp = std::to_string(bank.size());
+    for (const Sample& s : bank.all()) {
+        fp += '\x1f';
+        fp += s.id;
+        fp += '\x1f';
+        fp += s.relativePath;
+    }
+    return fp;
+}
+
+// Recomputes the fingerprint; on change, bumps the generation and clears the
+// cache (bounding memory and invalidating every stale-generation entry). Returns
+// true if the bank changed since last check.
+bool refreshFingerprint() {
+    if (!g_panel.session) return false;
+    std::string fp = bankFingerprint(g_panel.session->bank());
+    if (fp == g_panel.bankFingerprint) return false;
+    g_panel.bankFingerprint = std::move(fp);
+    ++g_panel.generation;
+    g_panel.cache.clear();
+    return true;
+}
+
+// --- Dialog proc + docking ----------------------------------------------------
+
+WDL_DLGRET dlgProc(HWND hwnd, UINT msg, WPARAM wParam, LPARAM lParam) {
+    switch (msg) {
+        case WM_PAINT: {
+            PAINTSTRUCT ps;
+            HDC hdc = BeginPaint(hwnd, &ps);
+            paintPanel(hwnd, hdc);
+            EndPaint(hwnd, &ps);
+            return 0;
+        }
+        case WM_DESTROY:
+            // REAPER closed the dock (user X'd it). Reflect closed state so the
+            // toggle re-opens rather than trying to reuse a dead HWND.
+            g_panel.hwnd = nullptr;
+            g_panel.open = false;
+            return 0;
+        default:
+            break;
+    }
+    return 0;
+}
+
+void openPanel() {
+    if (g_panel.open && g_panel.hwnd) {
+        DockWindowActivate(g_panel.hwnd);
+        return;
+    }
+    // Create the dialog as a child (WS_CHILD in the template); REAPER's docker
+    // reparents it. lParam is unused (state lives in g_panel).
+    g_panel.hwnd = CreateDialogParam(g_hInst, MAKEINTRESOURCE(IDD_BANK_PANEL),
+                                     GetMainHwnd(), dlgProc, 0);
+    if (!g_panel.hwnd) return;
+
+    // Dock it. identstr is a stable per-window key REAPER uses to remember the
+    // dock position/state across sessions; FOREVER-STABLE like the action ids.
+    // allowShow=true asks REAPER to show the dock if hidden.
+    DockWindowAddEx(g_panel.hwnd, "ReaSampler Bank", "reasampler_bank_panel", true);
+    DockWindowActivate(g_panel.hwnd);
+    g_panel.open = true;
+
+    // Prime the fingerprint so the first timer tick doesn't count the initial
+    // bank as a "change" (it's already drawn on open).
+    refreshFingerprint();
+}
+
+void closePanel() {
+    if (g_panel.hwnd) {
+        DockWindowRemove(g_panel.hwnd);
+        DestroyWindow(g_panel.hwnd);
+        g_panel.hwnd = nullptr;
+    }
+    g_panel.open = false;
+}
+
+}  // namespace
+
+// --- Public API ---------------------------------------------------------------
+
+void bankPanelInit(ReaSamplerSession* session) {
+    g_panel.session = session;
+}
+
+void bankPanelToggle() {
+    if (g_panel.open)
+        closePanel();
+    else
+        openPanel();
+}
+
+bool bankPanelIsOpen() {
+    return g_panel.open;
+}
+
+void bankPanelRefresh() {
+    if (!g_panel.open || !g_panel.hwnd) return;
+    // Repaint only when the bank actually changed (generation bump). Cheap tick
+    // otherwise — just a fingerprint string compare.
+    if (refreshFingerprint())
+        InvalidateRect(g_panel.hwnd, nullptr, FALSE);
+}
+
+void bankPanelShutdown() {
+    closePanel();
+    g_panel.cache.clear();
+    g_panel.session = nullptr;
+}
+
+}  // namespace reasampler

src/bank_panel.h

@@ -0,0 +1,41 @@
+#pragma once
+// bank_panel — the docked grid window (M5, Wave A). REAPER-facing shell: it owns
+// a SWELL dialog docked via DockWindowAddEx, and paints the current project's
+// bank as a grid of LICE-drawn waveform thumbnails. Read-only this wave: it NEVER
+// inserts into the arrange or mutates the project/bank (CONTEXT.md §load-bearing
+// principle). Audition / multi-select / keyboard nav are Wave B.
+//
+// The header is REAPER-free as practical: main.cpp drives the panel through these
+// free functions, passing the live session so the panel reads the current bank.
+// All SWELL / LICE / PCM_source use is confined to bank_panel.cpp. The pure
+// layout math and cache keys live in bank_grid (unit-tested outside the DAW).
+
+namespace reasampler {
+
+class ReaSamplerSession;
+
+// Wires the panel into main.cpp's lifecycle. Called once after the API pointers
+// are loaded, BEFORE the toggle action is registered. `session` must outlive the
+// panel (it is the extension-lifetime g_session). Stores the session pointer the
+// panel reads on every repaint; does not create the window yet.
+void bankPanelInit(ReaSamplerSession* session);
+
+// Toggles the docked window: creates+docks it if hidden, hides+undocks it if
+// shown. Bound to the "toggle bank panel" action. Safe to call before the first
+// timer tick.
+void bankPanelToggle();
+
+// Whether the panel window is currently open/visible. Feeds the action's
+// checked-state (toggleaction) so REAPER shows a tick next to the menu entry.
+bool bankPanelIsOpen();
+
+// Requests a repaint if the bank changed since the last paint (generation bump).
+// Cheap when nothing changed. Driven by the timer so a capture / project load is
+// reflected without the panel diffing the bank itself.
+void bankPanelRefresh();
+
+// Tears the panel down on extension unload: destroys the window and releases any
+// cached thumbnails / PCM handles. Mirror of bankPanelInit; safe if never opened.
+void bankPanelShutdown();
+
+} // namespace reasampler

src/main.cpp

@@ -21,6 +21,7 @@
 #include <string>
 
 #include "bank_model.h"
+#include "bank_panel.h"
 #include "capture.h"
 #include "persist.h"
 
@@ -44,6 +45,11 @@ reaper_plugin_info_t*   g_rec   = nullptr;  // REAPER's dispatch struct
 // (user keybindings key off it) — see the prefix note above.
 static int g_cmdCaptureMasterSpike = 0;
 
+// Command id for "ReaSampler: toggle bank panel" (M5). FOREVER-STABLE string.
+// The docked grid window is display-only this wave (Wave A) — the action just
+// shows/hides it; it never captures, inserts, or mutates the bank.
+static int g_cmdToggleBankPanel = 0;
+
 // The persistence session (M4): owns the in-memory BankIndex and bridges it to
 // project ext state. A timer tick drives g_session.poll() to detect project
 // load / Save-As; capture adds Samples to g_session.bank(); after a capture we
@@ -57,6 +63,10 @@ static reasampler::ReaSamplerSession g_session;
 static void OnTimer()
 {
     g_session.poll();
+    // Reflect a live bank change (capture / project load) in the docked grid.
+    // Cheap when the bank is unchanged (a fingerprint compare); repaints only on
+    // an actual change. No-op when the panel is closed.
+    reasampler::bankPanelRefresh();
 }
 
 // Runs the M3 spike: render the time-selection master mix, add the Sample, log.
@@ -107,11 +117,22 @@ static bool OnHookCommand(int command, int /*flag*/)
 {
     if (command == 0) return false;
     if (command == g_cmdCaptureMasterSpike) { RunCaptureMasterSpike(); return true; }
+    if (command == g_cmdToggleBankPanel)    { reasampler::bankPanelToggle(); return true; }
     return false;
 }
 
+// REAPER polls this to render each of OUR actions' checked state in menus/toolbars.
+// Return 1 (on) / 0 (off) for ids we own, -1 for everything else (per the contract).
+static int OnToggleAction(int command)
+{
+    if (command == g_cmdToggleBankPanel)
+        return reasampler::bankPanelIsOpen() ? 1 : 0;
+    return -1;  // not ours / non-toggling
+}
+
 // gaccel storage must outlive registration — REAPER holds the pointer.
 static gaccel_register_t g_accelCaptureMaster{};
+static gaccel_register_t g_accelToggleBankPanel{};
 
 extern "C" REAPER_PLUGIN_DLL_EXPORT int REAPER_PLUGIN_ENTRYPOINT(
     REAPER_PLUGIN_HINSTANCE hInstance, reaper_plugin_info_t* rec)
@@ -123,11 +144,18 @@ extern "C" REAPER_PLUGIN_DLL_EXPORT int REAPER_PLUGIN_ENTRYPOINT(
         if (g_rec)
         {
             g_rec->Register("-timer", (void*)&OnTimer);
+            g_rec->Register("-toggleaction", (void*)&OnToggleAction);
             g_rec->Register("-hookcommand", (void*)&OnHookCommand);
+            g_rec->Register("-gaccel", (void*)&g_accelToggleBankPanel);
+            g_rec->Register("-command_id",
+                            (void*)(REASAMPLER_ACTION_PREFIX "TOGGLE_BANK_PANEL"));
             g_rec->Register("-gaccel", (void*)&g_accelCaptureMaster);
             g_rec->Register("-command_id",
                             (void*)(REASAMPLER_ACTION_PREFIX "CAPTURE_MASTER_SPIKE"));
         }
+        // Destroy the docked window and release cached thumbnails before we drop
+        // the API pointers (DockWindowRemove/DestroyWindow need them live).
+        reasampler::bankPanelShutdown();
         g_rec = nullptr;
         return 0;
     }
@@ -153,9 +181,30 @@ extern "C" REAPER_PLUGIN_DLL_EXPORT int REAPER_PLUGIN_ENTRYPOINT(
         g_accelCaptureMaster.accel.cmd = g_cmdCaptureMasterSpike;
         g_accelCaptureMaster.desc      = "ReaSampler: capture master mix (spike)";
         rec->Register("gaccel", (void*)&g_accelCaptureMaster);
-        rec->Register("hookcommand", (void*)&OnHookCommand);
     }
 
+    // Point the bank panel at the live session BEFORE registering its action, so
+    // a toggle firing immediately has a session to read (M5). Does not open the
+    // window — only stores the session pointer.
+    reasampler::bankPanelInit(&g_session);
+
+    // Register the M5 "toggle bank panel" action (command_id -> gaccel ->
+    // hookcommand + toggleaction for the checked state).
+    g_cmdToggleBankPanel = rec->Register(
+        "command_id",
+        (void*)(REASAMPLER_ACTION_PREFIX "TOGGLE_BANK_PANEL"));
+    if (g_cmdToggleBankPanel)
+    {
+        g_accelToggleBankPanel.accel.cmd = g_cmdToggleBankPanel;
+        g_accelToggleBankPanel.desc      = "ReaSampler: toggle bank panel";
+        rec->Register("gaccel", (void*)&g_accelToggleBankPanel);
+        rec->Register("toggleaction", (void*)&OnToggleAction);
+    }
+
+    // One hookcommand routes every ReaSampler action (spike + toggle). Registered
+    // once, after both command ids are minted.
+    rec->Register("hookcommand", (void*)&OnHookCommand);
+
     // Drive project-load / Save-As detection (M4 persist). The timer polls the
     // active project each tick; on a project load it reloads the bank from ext
     // state, on a Save-As it relocates the bank folder under the new .rpp.

src/peaks.cpp

@@ -14,7 +14,7 @@
 
 namespace reasampler {
 
-Envelope computeEnvelope(const std::vector<Sample>& interleaved,
+Envelope computeEnvelope(const std::vector<AudioSample>& interleaved,
                          std::size_t channelCount,
                          std::size_t frameCount,
                          std::size_t binCount) {
@@ -48,11 +48,11 @@ Envelope computeEnvelope(const std::vector<Sample>& interleaved,
                 continue; // empty span (binCount > frames) -> keep {0,0}
             }
 
-            const Sample first = interleaved[begin * channelCount + ch];
-            Sample lo = first;
-            Sample hi = first;
+            const AudioSample first = interleaved[begin * channelCount + ch];
+            AudioSample lo = first;
+            AudioSample hi = first;
             for (std::size_t f = begin + 1; f < end; ++f) {
-                const Sample s = interleaved[f * channelCount + ch];
+                const AudioSample s = interleaved[f * channelCount + ch];
                 lo = std::min(lo, s);
                 hi = std::max(hi, s);
             }

src/peaks.h

@@ -13,18 +13,23 @@
 
 namespace reasampler {
 
-// Canonical in-memory sample type. `float` is REAPER's native audio buffer format
-// (its render/PCM_source callbacks hand back interleaved 32-bit float), so peaks
-// consumes that directly with no lossy conversion. If a capture ever lands as a
-// different depth, the caller converts to float at the boundary — the thumbnail
-// core stays single-typed.
-using Sample = float;
+// Canonical in-memory audio-sample type. `float` is REAPER's native audio buffer
+// format (its render/PCM_source callbacks hand back interleaved 32-bit float), so
+// peaks consumes that directly with no lossy conversion. If a capture ever lands
+// as a different depth, the caller converts to float at the boundary — the
+// thumbnail core stays single-typed.
+//
+// NAMED AudioSample, not `Sample`: `reasampler::Sample` is already bank_model's
+// metadata struct. A `using Sample = float` here would collide at namespace scope
+// wherever both headers are visible (the bank_panel module includes both). The
+// audio-domain name also reads more precisely — this is one PCM sample value.
+using AudioSample = float;
 
 // One bin of a channel's envelope: the extremes of every sample that fell in it.
 // min <= max always. For an empty bin (more bins than frames), both are 0.
 struct MinMax {
-    Sample min = 0.0f;
-    Sample max = 0.0f;
+    AudioSample min = 0.0f;
+    AudioSample max = 0.0f;
 
     bool operator==(const MinMax& o) const { return min == o.min && max == o.max; }
 };
@@ -56,7 +61,7 @@ using Envelope = std::vector<ChannelEnvelope>;
 //   binCount == 0     -> per channel: an empty bin vector.
 //   channelCount == 0 -> an empty envelope (no channels).
 //   frameCount == 0   -> per channel: binCount bins, all {0, 0}.
-Envelope computeEnvelope(const std::vector<Sample>& interleaved,
+Envelope computeEnvelope(const std::vector<AudioSample>& interleaved,
                          std::size_t channelCount,
                          std::size_t frameCount,
                          std::size_t binCount);

src/resource.h

@@ -0,0 +1,10 @@
+#pragma once
+// resource.h — dialog/control ids for ReaSampler's SWELL dialogs.
+//
+// Shared by resource.rc (Windows resource compiler) and, on macOS/Linux, by the
+// SWELL resgen-generated source (see CLAUDE.md §SWELL dialog resources). Keep the
+// numeric ids stable and unique across the extension.
+
+// The docked bank panel (M5). A bare owner-drawn child dialog: it carries no
+// controls — bank_panel.cpp paints the whole client area with LICE.
+#define IDD_BANK_PANEL 1000

src/resource.rc

@@ -0,0 +1,22 @@
+// resource.rc — SWELL/Win32 dialog templates for ReaSampler.
+//
+// Windows: compiled by the platform resource compiler (MSVC rc / windres) and
+// linked into reaper_reasampler.
+// macOS/Linux: pre-processed once by SWELL's resgen into a C++ source that is
+// added to the module target (see CLAUDE.md §SWELL dialog resources / README).
+//
+// IDD_BANK_PANEL is a bare child dialog with no controls: the bank_panel shell
+// owns every pixel and draws the sample grid with LICE in WM_PAINT. It is created
+// as a child (WS_CHILD) so REAPER's docker can reparent it into a dock.
+
+#include "resource.h"
+
+#ifdef _WIN32
+#include <windows.h>
+#endif
+
+IDD_BANK_PANEL DIALOG DISCARDABLE 0, 0, 400, 300
+STYLE WS_CHILD
+FONT 8, "MS Shell Dlg"
+BEGIN
+END

tests/test_bank_grid.cpp

@@ -0,0 +1,144 @@
+// Standalone tests for reasampler::bank_grid — no REAPER, no test framework.
+// Same fast loop as the sibling pure tests: assert the grid-layout math and the
+// thumbnail cache-key stringification directly.
+//
+// Covers (M5 Wave A brief §Test cases): column count for a given panel width;
+// cell rects for a full grid (row/column wrapping); the partial-last-row case;
+// itemCount == 0; a single item; a panel too narrow for even one cell (clamp to
+// one column); content-height for exact and partial rows; cache-key stability,
+// width/generation/id sensitivity, and length-prefix collision resistance.
+
+#include "../src/bank_grid.h"
+
+#include <cstdio>
+#include <string>
+#include <vector>
+
+using namespace reasampler;
+
+static int g_fail = 0;
+#define CHECK(cond) do { if(!(cond)) { \
+    std::printf("FAIL line %d: %s\n", __LINE__, #cond); ++g_fail; } } while(0)
+
+// A spec with round numbers so expected rects are trivial to hand-compute:
+// cell 100x50, gap 10. Column pitch = 110, row pitch = 60, margin = 10.
+static GridSpec spec() {
+    GridSpec s;
+    s.cellWidth = 100;
+    s.cellHeight = 50;
+    s.gap = 10;
+    return s;
+}
+
+// gap(10) + n*(100+10): 1 col needs 120, 2 need 230, 3 need 340.
+static void testColumnsForWidth() {
+    const GridSpec s = spec();
+    CHECK(columnsForWidth(120, s) == 1);   // exactly one cell + margins
+    CHECK(columnsForWidth(229, s) == 1);   // one pixel short of two columns
+    CHECK(columnsForWidth(230, s) == 2);   // exactly two
+    CHECK(columnsForWidth(345, s) == 3);   // three plus slack
+    CHECK(columnsForWidth(1000, s) == 9);  // many
+}
+
+// A panel narrower than a single cell still yields one column (clipped by the
+// window, never zero — that would drop every sample).
+static void testTooNarrowClampsToOneColumn() {
+    const GridSpec s = spec();
+    CHECK(columnsForWidth(50, s) == 1);
+    CHECK(columnsForWidth(0, s) == 1);
+    CHECK(columnsForWidth(-20, s) == 1);
+}
+
+// Zero items -> no rects (empty state is the panel's concern, not the layout's).
+static void testZeroItems() {
+    const GridSpec s = spec();
+    auto rects = computeCellRects(0, 500, s);
+    CHECK(rects.empty());
+    CHECK(contentHeight(0, 500, s) == 0);
+}
+
+// One item sits at the top-left margin.
+static void testSingleItem() {
+    const GridSpec s = spec();
+    auto rects = computeCellRects(1, 500, s);
+    CHECK(rects.size() == 1);
+    CHECK(rects[0] == (CellRect{10, 10, 100, 50}));
+}
+
+// A full 2x2: width forces exactly two columns, four items fill two rows.
+static void testFullGridWrapping() {
+    const GridSpec s = spec();
+    // Width 230 -> exactly 2 columns.
+    auto rects = computeCellRects(4, 230, s);
+    CHECK(rects.size() == 4);
+    // Row 0: x = 10, 120 ; y = 10.
+    CHECK(rects[0] == (CellRect{10, 10, 100, 50}));
+    CHECK(rects[1] == (CellRect{120, 10, 100, 50}));
+    // Row 1: y = 70 (10 + 60).
+    CHECK(rects[2] == (CellRect{10, 70, 100, 50}));
+    CHECK(rects[3] == (CellRect{120, 70, 100, 50}));
+}
+
+// Partial last row: 5 items in a 2-column grid -> rows of 2,2,1. The lone last
+// cell is left-aligned in its row (no centering), same x as column 0.
+static void testPartialLastRow() {
+    const GridSpec s = spec();
+    auto rects = computeCellRects(5, 230, s);  // 2 columns
+    CHECK(rects.size() == 5);
+    CHECK(rects[4] == (CellRect{10, 130, 100, 50}));  // row 2, col 0: y = 10 + 2*60
+    // content height spans 3 rows: 10 + 3*(50+10) = 190.
+    CHECK(contentHeight(5, 230, s) == 190);
+}
+
+// Content height for an exact-fill grid: 4 items / 2 cols = 2 rows.
+static void testContentHeightExactRows() {
+    const GridSpec s = spec();
+    CHECK(contentHeight(4, 230, s) == 130);  // 10 + 2*60
+    CHECK(contentHeight(2, 230, s) == 70);   // 10 + 1*60
+}
+
+// The cache key is stable and sensitive to every field.
+static void testCacheKeyStabilityAndSensitivity() {
+    ThumbnailKey a{"sample-1", 120, 7};
+    ThumbnailKey aSame{"sample-1", 120, 7};
+    CHECK(thumbnailKeyString(a) == thumbnailKeyString(aSame));  // deterministic
+
+    ThumbnailKey diffWidth{"sample-1", 121, 7};
+    ThumbnailKey diffGen{"sample-1", 120, 8};
+    ThumbnailKey diffId{"sample-2", 120, 7};
+    CHECK(thumbnailKeyString(a) != thumbnailKeyString(diffWidth));
+    CHECK(thumbnailKeyString(a) != thumbnailKeyString(diffGen));
+    CHECK(thumbnailKeyString(a) != thumbnailKeyString(diffId));
+}
+
+// A sampleId containing the delimiter byte must not forge a collision with a
+// different key. Without the length prefix, id "x|9" with width 0 and id "x" with
+// width 9 would both tail-concatenate through the '|' delimiter and could match;
+// the length prefix on the id disambiguates them.
+static void testCacheKeyDelimiterCollisionResistance() {
+    // The canonical would-be collision: moving a "|9" fragment from the id into
+    // the width field. Length-prefixing the id makes the two forms distinct.
+    ThumbnailKey a{"x|9", 0, 0};
+    ThumbnailKey b{"x", 9, 0};
+    CHECK(thumbnailKeyString(a) != thumbnailKeyString(b));
+
+    // A second pair in the same spirit, delimiters in both id and adjacent fields.
+    ThumbnailKey k1{"1|2", 3, 0};
+    ThumbnailKey k2{"1", 23, 0};
+    CHECK(thumbnailKeyString(k1) != thumbnailKeyString(k2));
+}
+
+int main() {
+    testColumnsForWidth();
+    testTooNarrowClampsToOneColumn();
+    testZeroItems();
+    testSingleItem();
+    testFullGridWrapping();
+    testPartialLastRow();
+    testContentHeightExactRows();
+    testCacheKeyStabilityAndSensitivity();
+    testCacheKeyDelimiterCollisionResistance();
+
+    if (g_fail == 0) std::printf("All tests passed.\n");
+    return g_fail ? 1 : 0;
+}

tests/test_peaks.cpp

@@ -27,8 +27,8 @@ constexpr double kPi = 3.14159265358979323846;
 
 // A full-scale sine over `frames` frames, mono, `cycles` complete periods so every
 // bin sees both a near-peak and a near-trough.
-static std::vector<Sample> monoSine(std::size_t frames, double cycles, float amp) {
-    std::vector<Sample> buf(frames);
+static std::vector<AudioSample> monoSine(std::size_t frames, double cycles, float amp) {
+    std::vector<AudioSample> buf(frames);
     for (std::size_t i = 0; i < frames; ++i) {
         const double phase = 2.0 * kPi * cycles * (double)i / (double)frames;
         buf[i] = amp * (float)std::sin(phase);
@@ -60,7 +60,7 @@ static void testSineEnvelope() {
 static void testRampMonotonic() {
     const std::size_t frames = 10000;
     const std::size_t bins = 50;
-    std::vector<Sample> buf(frames);
+    std::vector<AudioSample> buf(frames);
     for (std::size_t i = 0; i < frames; ++i) {
         buf[i] = (float)i / (float)(frames - 1); // 0.0 .. 1.0
     }
@@ -97,14 +97,14 @@ static void testDcAndSilence() {
     const std::size_t frames = 1000;
     const std::size_t bins = 16;
 
-    std::vector<Sample> silence(frames, 0.0f);
+    std::vector<AudioSample> silence(frames, 0.0f);
     Envelope se = computeEnvelope(silence, 1, frames, bins);
     for (const MinMax& mm : se[0]) {
         CHECK(mm.min == 0.0f);
         CHECK(mm.max == 0.0f);
     }
 
-    std::vector<Sample> dc(frames, 0.5f);
+    std::vector<AudioSample> dc(frames, 0.5f);
     Envelope de = computeEnvelope(dc, 1, frames, bins);
     for (const MinMax& mm : de[0]) {
         CHECK(mm.min == 0.5f);
@@ -121,7 +121,7 @@ static void testMultiChannelNoFold() {
 
     // Interleave: [ch0, ch1] per frame; ch0 = sine, ch1 = 0.
     auto sine = monoSine(frames, /*cycles=*/64.0, amp);
-    std::vector<Sample> buf(frames * 2);
+    std::vector<AudioSample> buf(frames * 2);
     for (std::size_t i = 0; i < frames; ++i) {
         buf[i * 2 + 0] = sine[i];
         buf[i * 2 + 1] = 0.0f;
@@ -147,7 +147,7 @@ static void testMultiChannelNoFold() {
 static void testChannelsNotAveraged() {
     const std::size_t frames = 100;
     const std::size_t bins = 4;
-    std::vector<Sample> buf(frames * 2);
+    std::vector<AudioSample> buf(frames * 2);
     for (std::size_t i = 0; i < frames; ++i) {
         buf[i * 2 + 0] = 1.0f;
         buf[i * 2 + 1] = -1.0f;
@@ -164,7 +164,7 @@ static void testChannelsNotAveraged() {
 static void testShortBuffer() {
     const std::size_t frames = 3;
     const std::size_t bins = 8;
-    std::vector<Sample> buf = {0.25f, -0.5f, 0.75f};
+    std::vector<AudioSample> buf = {0.25f, -0.5f, 0.75f};
 
     Envelope env = computeEnvelope(buf, 1, frames, bins);
     CHECK(env[0].size() == bins);
@@ -190,7 +190,7 @@ static void testShortBuffer() {
 static void testNonDivisibleRemainderBin() {
     const std::size_t frames = 10;
     const std::size_t bins = 3;
-    std::vector<Sample> buf(frames);
+    std::vector<AudioSample> buf(frames);
     for (std::size_t i = 0; i < frames; ++i) buf[i] = (float)i; // 0..9
 
     Envelope env = computeEnvelope(buf, 1, frames, bins);
@@ -205,7 +205,7 @@ static void testNonDivisibleRemainderBin() {
 
 // binCount == 1: the whole buffer collapses to a single min/max.
 static void testSingleBinWholeBuffer() {
-    std::vector<Sample> buf = {-0.3f, 0.8f, -0.9f, 0.1f, 0.4f};
+    std::vector<AudioSample> buf = {-0.3f, 0.8f, -0.9f, 0.1f, 0.4f};
     Envelope env = computeEnvelope(buf, 1, buf.size(), 1);
     CHECK(env[0].size() == 1);
     CHECK(env[0][0].min == -0.9f);
@@ -214,7 +214,7 @@ static void testSingleBinWholeBuffer() {
 
 // Degenerate inputs: defined behavior, no UB, no throw.
 static void testDegenerateInputs() {
-    std::vector<Sample> buf = {0.1f, 0.2f, 0.3f, 0.4f};
+    std::vector<AudioSample> buf = {0.1f, 0.2f, 0.3f, 0.4f};
 
     // Zero frames -> binCount bins, all {0,0}.
     Envelope zf = computeEnvelope(buf, 1, 0, 4);
@@ -238,7 +238,7 @@ static void testDegenerateInputs() {
     CHECK(over[0][1].min == 0.3f && over[0][1].max == 0.4f);
 
     // Empty buffer, non-zero request -> all-zero bins, no crash.
-    std::vector<Sample> empty;
+    std::vector<AudioSample> empty;
     Envelope eb = computeEnvelope(empty, 2, 10, 3);
     CHECK(eb.size() == 2);
     for (const auto& chenv : eb) {
@@ -257,7 +257,7 @@ static void testLargeBinCountOverflowGuard() {
     // same loop iteration path that would UB for pathological binCount near SIZE_MAX.
     const std::size_t frames = 4;
     const std::size_t binCount = 9;
-    std::vector<Sample> buf = {0.1f, 0.2f, 0.3f, 0.4f};
+    std::vector<AudioSample> buf = {0.1f, 0.2f, 0.3f, 0.4f};
 
     Envelope env = computeEnvelope(buf, 1, frames, binCount);
     CHECK(env.size() == 1);