fix: prevent cross-context bleed and repetition loops in inline suggestions

[shreeraman96]

Fixes #32.

Inline suggestions could surface text the user never typed in the focused field (leaking across windows, apps, and browser tabs) and could loop on already-written phrases. The causes were spread across the OCR window picker, the output filter, writing-history selection, and the reuse cache. This adds layered, independently-testable guards plus the missing scoping.

Changes

Cross-window OCR — ScreenWindowSelector, WindowOCRCaptureEngine, ScreenContextController

• Select the window under the caret, not just the largest. The caret point is converted AppKit→CG (new DisplayCoordinateConverter.coreGraphicsPoint) so it matches SCWindow.frame's coordinate space.
• Tie-break by z-order (frontmost) so an overlapping background window can't win.
• Clear the cached OCR text on window/tab change so a stale reading from the previous window can't be injected before the fresh capture lands.

Repetition loops — PrefixRepetitionGuard (new)

• Suppress a completion reproducing a recent phrase from beforeCursor, catching both whole-completion repeats and leading repeats that then diverge.

Cross-app / cross-tab writing history — CompletionController, WritingHistory, PersistentWritingHistoryStore

• Scope previousUserInputs to the same app and, for web fields, the same domain, so another app/tab's content can't be injected and parroted. Empty domains are normalized to nil.

Clipboard / OCR echo — ContextEchoGuard (new)

• Suppress a completion that verbatim-reproduces injected side context (clipboard / on-screen OCR) the user did not type. Writing history is intentionally excluded — it is scoped, and echoing the user's own recurring phrases is the point of that feature.

Reuse cache — CompletionController

• Re-check the context-dependent guards (prefix-repetition, suffix-overlap, echo) against the live context before re-showing a cached completion, so reuse can't bypass them as beforeCursor/clipboard change.

Refactor

• Extract AlphanumericNormalizer + RepeatedSpanDetector, shared by the overlap guards (removes a duplicated normalizer).

Tests

New/extended unit tests across all of the above: caret→window selection incl. frontmost/overlap and AppKit↔CG round-trip on multi-display; prefix-repetition (whole + leading, boundary cases); context-echo; same-app + same-domain history scoping (in-memory and DB-level); heal-aware filtering; and reuse-path re-checks.

All Swift package suites pass (AutocompleteCore, MacContextCapture, ConstrainedGeneration, Personalization, Prompting) and the app target builds. Rebased on latest main (incl. the re-optimized mid-line completions work).

Notes

• Touches opt-in features (Screen-context OCR, clipboard context, writing history).
• The fixes are intentionally layered (selection scoping + output guards + cache re-check) so a miss in one layer is caught by another.

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