Context

PR #653 added chunk_progress SSE events to the indexing stream and surfaced them in the Index tab as file.md — 100/250 chunks. The Sources → Memory Dirs reindex flow consumes the same stream (sources-memory-dirs.js mdReindexOne, line 1093-1177), but PR #653 deliberately left it untouched because the per-button text already reads 5/12 and adding 5/12 — 100/250 would crowd or wrap the button.

This issue tracks the design-and-implement work for chunk-level visibility in that flow.

Why this needs design, not just code

The Memory Dirs button is a small, fixed-width control inside a row of vendor cards. Naive concatenation breaks the layout. Options that need a decision:

1. Two-line button — file count on top, chunk count below. Costs vertical space across the entire dirs list.
2. Tooltip / aria-label — hover/focus shows 5/12 files, 100/250 chunks. Keeps button text untouched but accessibility-only.
3. Replace button text mid-flight — show only 100/250 chunks while a single file is in-flight, snap back to N/M once the file completes. Most informative but visually noisy.
4. Inline progress bar under the button — full bar like the Index tab. Most consistent UX but the largest layout change.

Acceptance criteria

• During a Memory Dirs reindex, the user can see per-chunk progress for the file currently being embedded — no requirement on the exact form.
• Existing 5/12 file counter behavior preserved (or knowingly replaced).
• Layout does not wrap or shift adjacent dirs cards on any of: 1280px, 1024px, narrow mobile.
• Throttle (~100ms) and final-tick (done == total) bypass match the Index tab's behavior — copy/paste from app.js:runIndexStream is fine.
• No new SSE event types needed; consume the existing chunk_progress event from the stream.

Files likely touched

• packages/memtomem/src/memtomem/web/static/sources-memory-dirs.js (mdReindexOne, line 1093-1177)
• packages/memtomem/src/memtomem/web/static/style.css (if option 1 or 4)
• packages/memtomem/src/memtomem/web/static/locales/en.json + ko.json (new label key)

References

• PR feat(indexing): per-chunk progress events for SSE indexing stream #653 (parent feature)
• feedback_layout_primitives_first.md pattern — check existing .dir-button / .reindex-btn overflow rules before adding new CSS.