feat(overlay): show popup card when caret is mid-line

[FuJacob]

Summary

When the caret sits mid-line (real characters follow it before the next line break), inline ghost text has no home: it would render on top of the text after the caret. This promotes any such presentation to the popup (mirror) card instead, anchored to the caret line. It is the first step toward fill-in-middle (FIM) completions, which structurally need the card because a mid-line completion cannot be drawn inline.

The signal is the existing CaretLinePosition.isAtEndOfLine, so an end-of-line caret that still has later paragraphs below it stays inline (only same-line trailing characters trigger the card).

Validation

swiftlint lint --quiet <6 changed source files>
# exit 0

xcodebuild -project Cotabby.xcodeproj -scheme Cotabby -destination 'platform=macOS' \
  build-for-testing -derivedDataPath build/DerivedData CODE_SIGNING_ALLOWED=NO CODE_SIGNING_REQUIRED=NO
# ** TEST BUILD SUCCEEDED **

xcodebuild test-without-building ... \
  -only-testing:CotabbyTests/CompletionRenderModePolicyTests \
  -only-testing:CotabbyTests/CaretLinePositionTests \
  -only-testing:CotabbyTests/MirrorOverlayLayoutTests
# Executed 39 tests, with 0 failures

App-hosted tests were run locally with signing disabled. The 7 new policy tests cover the auto / always-inline / always-mirror / per-app-override matrix at both end-of-line and mid-line carets; existing policy, caret-position, and mirror-layout suites still pass.

Linked issues

No issue number provided. Groundwork for FIM completions.

Risk / rollout notes

• Behavior change to an existing flow: a suggestion generated with the caret mid-line (e.g. the mid-word continuations that already fire via MidWordContinuationPolicy) previously rendered as inline ghost text overlapping the trailing characters. It now renders in the popup card. This is a net improvement for that case, but it is a visible change.
• The mid-line rule deliberately overrides an explicit "Inline" appearance preference, because inline cannot render mid-line without overlap. If we would rather honor the pin and leave those users on inline mid-line, the override is a one-line change in CompletionRenderModePolicy.mode (gate the promotion on .auto only). Flagging for a product call.
• No schema, settings, or project.yml / pbxproj migrations. No new files (test changes live in existing files, so XcodeGen does not drift).
• Mirror-card anchoring for the new .caretMidLine reason reuses the trustworthy-geometry path (anchors to the caret line), so there is no new positioning math.

Greptile Summary

This PR introduces mid-line caret detection into the completion render-mode pipeline: when isCaretAtEndOfLine is false, any inline result is promoted to the popup (mirror) card via the new .caretMidLine reason, preventing ghost text from painting over trailing characters and laying the groundwork for fill-in-middle completions.

• Adds isCaretAtEndOfLine: Bool (default true) to SuggestionOverlayGeometry and threads it from FocusedInputContext through SuggestionCoordinator+Acceptance.
• Refactors CompletionRenderModePolicy.mode into a thin wrapper + a private preferenceMode, with the mid-line promotion expressed as a single, well-scoped guard; MirrorOverlayLayout.computeAnchorTopY groups .caretMidLine with the other trustworthy-geometry reasons and anchors to the caret rect.
• Adds 7 new policy tests covering the auto / alwaysInline / alwaysMirror / per-app-override matrix at both end-of-line and mid-line carets, including the important "estimated geometry keeps its own reason" invariant.

Confidence Score: 5/5

Safe to merge; the behavior change (mid-line inline → popup card) is intentional, the promotion is correctly scoped to inline-only base modes, and the prior inline path is preserved by a safe default.

The policy refactor is small and well-contained: preferenceMode is the unchanged original logic, and the new wrapper adds a single, clearly-guarded promotion. The isCaretAtEndOfLine default of true ensures all pre-existing call sites keep their prior behavior. The 7 new tests cover the full preference × caret-position matrix, including the estimated-geometry invariant and the alwaysInline override case. No schema, persistence, or migration changes are involved.

No files require special attention.

Important Files Changed

Filename	Overview
Cotabby/Support/CompletionRenderModePolicy.swift	Public mode is now a thin wrapper that calls the renamed private preferenceMode and applies the mid-line promotion; logic is clean and all test scenarios pass.
Cotabby/Models/SuggestionModels.swift	Adds isCaretAtEndOfLine: Bool = true to SuggestionOverlayGeometry; default preserves prior inline behavior for existing call sites, and replacingCaretRect correctly forwards the value.
Cotabby/Support/MirrorOverlayLayout.swift	computeAnchorTopY groups .caretMidLine with .userPreference and .perAppOverride for caret-rect anchoring; doc comment updated accordingly.
Cotabby/Models/CompletionRenderMode.swift	New .caretMidLine reason added to MirrorReason with accurate doc comment describing caret-rect anchoring behavior.
Cotabby/App/Coordinators/SuggestionCoordinator+Acceptance.swift	Passes isCaretAtEndOfLine: context.isCaretAtEndOfLine to SuggestionOverlayGeometry; single-line, correct change.
CotabbyTests/CompletionRenderModePolicyTests.swift	Seven new tests cover the full preference × caret-position matrix, including the subtle "estimated geometry keeps its reason" and "alwaysInline is overridden mid-line" invariants.
CotabbyTests/CotabbyTestFixtures.swift	Fixture overlayGeometry gains isCaretAtEndOfLine parameter (default true) matching the production default.

Flowchart

%%{init: {'theme': 'neutral'}}%%
flowchart TD
    A[SuggestionCoordinator\nreceives context] --> B[Build SuggestionOverlayGeometry\nwith isCaretAtEndOfLine]
    B --> C[CompletionRenderModePolicy\n.mode for:bundleIdentifier:]
    C --> D[preferenceMode\npreference + caretQuality]
    D --> E{baseMode == .inline?}
    E -- No --> F[Return baseMode\ne.g. .mirror caretGeometryEstimated\nor .mirror userPreference]
    E -- Yes --> G{isCaretAtEndOfLine?}
    G -- true --> H[Return .inline]
    G -- false --> I[Return .mirror reason: .caretMidLine]
    H --> J[MirrorOverlayLayout\nno card shown]
    I --> K[MirrorOverlayLayout\ncomputeAnchorTopY]
    F --> K
    K --> L{reason}
    L -- caretGeometryEstimated --> M[Anchor to inputFieldRect\nwith vertical slack offset]
    L -- userPreference / perAppOverride / caretMidLine --> N[Anchor to caretRect\nfield rect as fallback]

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_{Reviews (2): Last reviewed commit: "docs: correct caretMidLine anchor commen..." | Re-trigger Greptile}