Following a redline through the engine

The path a draft takes from baseline-plus-current text to email-safe redline HTML — the doc section first, then the modules that do the work.

Workflow 1 — Draft redline (Start tracking → Insert Redline)

State lives in src/hooks/useTracking.ts: a TrackingSnapshot (baseline + optional selection anchors), a loadingAction flag, and redlineInserted.

sequenceDiagram
  participant U as User
  participant H as useTracking
  participant O as src/outlook
  participant R as src/redline
  U->>H: Start tracking
  H->>O: getSelectedText() + getBodyHtml()
  alt selection made
    O-->>H: captureComposeSelectionAnchors()<br/>(48-char prefix/suffix anchors)
    H->>H: snapshot {scope:'selection', anchors, baselineHtml}
  else no selection
    H->>H: snapshot {scope:'full', baselineHtml}
  end
  U->>U: edits draft freely in Outlook
  U->>H: Insert Redline
  H->>O: getBodyHtml() (current state)
  alt selection scope
    O-->>H: extractRegionHtml(bodyHtml, anchors)
    H->>R: buildRegionRedline(baseline, currentRegion)
    R-->>H: redline HTML
    H->>O: replaceRegionInHtml(...) → setBodyHtml()
  else full scope
    H->>R: buildFullDraftRedline(baseline, bodyHtml)
    R-->>H: redline HTML (envelope preserved)
    H->>O: setBodyHtml(result.html)
  end

The body-region system (src/outlook/bodyRegion.ts) is what lets a selection survive the user's edits: at capture time it stores 48-character prefix/suffix anchors plus plain-text offsets (ANCHOR_LEN = 48, line 19); at insert time it relocates the region with a 512-char hint window (REGION_HINT_WINDOW = 512, line 20), line-ending normalization, and bullet-prefix-tolerant fuzzy matching, then splices the redline back into the full body HTML without disturbing blocks outside the region (replaceRegionInHtml, src/outlook/bodyRegion.ts:930).