feat(settings): add opt-in trailing space after accepting a suggestion

[FuJacob]

Summary

Adds a new opt-in "Add Space After Accepting" toggle (Settings → General → Behavior). When on, accepting a suggestion that finishes a word also types a trailing space so the user can keep typing without reaching for the space bar. This was a requested feature; it's off by default so existing WYSIWYG accept behavior is unchanged unless opted into.

The space is only appended when the accept exhausts the suggestion (the final chunk) — a mid-suggestion word accept is already followed by the next chunk's own leading space, so a space there would double up. Exhaustion is predicted the same way commitAcceptedChunk decides it (session.advancing(by:).isExhausted). The space is suppressed when the inserted text ends in punctuation (done., (yes), really?!), whitespace, or a space-less script (CJK/Thai never separate words with spaces), reusing the existing isAcceptanceWordCharacter / beginsSpacelessScriptWord primitives. Session accounting still advances by the unchanged acceptedChunk, and the session tears down on exhaustion, so the extra space never disturbs consumed-suffix reconciliation.

Validation

xcodebuild -project Cotabby.xcodeproj -scheme Cotabby -destination 'platform=macOS' build -derivedDataPath build/DerivedData
# ** BUILD SUCCEEDED **

xcodebuild ... test -only-testing:CotabbyTests/SuggestionSessionReconcilerTests CODE_SIGNING_ALLOWED=NO CODE_SIGNING_REQUIRED=NO
# ** TEST SUCCEEDED **  93 tests, 0 failures (includes 6 new tests for the pure helper)

xcodebuild ... test -only-testing:CotabbyTests/SettingsIndexTests -only-testing:CotabbyTests/SuggestionCoordinatorAcceptanceTests CODE_SIGNING_ALLOWED=NO CODE_SIGNING_REQUIRED=NO
# ** TEST SUCCEEDED **

swiftlint lint --quiet  # on all changed files, exit 0

Pure rule lives in SuggestionSessionReconciler.insertionChunkAppendingTrailingSpace(_:) (Support/), covered by new unit tests for word/digit/punctuation/whitespace/CJK/empty cases. The coordinator gates it via a small insertionTextApplyingAutoSpace(...) helper (kept separate so acceptSuggestion stays under the cyclomatic-complexity limit).

Linked issues

Risk / rollout notes

• New persisted setting: UserDefaults key cotabbyAddSpaceAfterAccept, defaults to false, so no behavior change for existing installs until opted in. Threaded through the full settings stack (data → store load/write-back/save → model @Published/setter/snapshot/Combine publisher → snapshot struct → UI toggle → search index).
• The new Combine upstream is paired with the existing trailing-punctuation toggle inside the timing tuple's last slot to stay under Combine's four-input CombineLatest cap.
• No project.yml/pbxproj changes (new test code is auto-discovered by folder).

Greptile Summary

This PR adds an opt-in "Add Space After Accepting" toggle in Settings → General → Behavior. When enabled, accepting the final chunk of a suggestion appends a trailing space, letting users continue typing without pressing Space. The setting defaults to false so no behavior change occurs for existing installs.

• The pure suppression rule lives in SuggestionSessionReconciler.insertionChunkAppendingTrailingSpace, which skips the space for text ending in punctuation, whitespace, or a spaceless-script (CJK/Thai) glyph; 6 new unit tests cover every branch.
• Exhaustion is predicted with session.advancing(by: acceptedChunk.count).isExhausted before commitAcceptedChunk, matching the same logic, so a mid-suggestion accept (where the next chunk already carries a leading space) never receives a doubled space. Session accounting still advances by the unmodified acceptedChunk, keeping consumed-suffix reconciliation intact.

Confidence Score: 5/5

Safe to merge — the feature is off by default, exhaustion prediction uses the same advancing logic as the actual commit, and suppression guards (punctuation, whitespace, CJK) are fully unit-tested.

The acceptance coordinator carefully predicts exhaustion before inserting so the space is never appended to a mid-suggestion chunk, and session accounting still advances by the unmodified acceptedChunk, keeping consumed-suffix reconciliation intact. The new setting is opt-in with a false default, so existing installs see no change. The pure helper function is isolated in SuggestionSessionReconciler with comprehensive unit tests, and the Combine publisher nesting to stay within the four-input cap follows the established codebase pattern.

No files require special attention.

Important Files Changed

Filename	Overview
Cotabby/App/Coordinators/SuggestionCoordinator+Acceptance.swift	Adds insertionTextApplyingAutoSpace helper before insertion; exhaustion prediction matches commitAcceptedChunk logic; presentAdvancedOverlay correctly keeps using insertionChunk (only reachable when not exhausted, so insertionText == insertionChunk there).
Cotabby/Support/SuggestionSessionReconciler.swift	New pure static method insertionChunkAppendingTrailingSpace correctly suppresses trailing space for empty chunks, punctuation, whitespace, and CJK/spaceless-script glyphs using existing isAcceptanceWordCharacter / beginsSpacelessScriptWord primitives.
Cotabby/Models/SuggestionSettingsModel.swift	Adds addSpaceAfterAccept @published property, threads it through the snapshot builder, and pairs it with autoAcceptTrailingPunctuation in a nested CombineLatest to stay within Combine's four-input cap — pattern is consistent with other recently added toggles.
Cotabby/Support/SuggestionSettingsStore.swift	New UserDefaults key cotabbyAddSpaceAfterAccept with explicit false default; load, save, and write-back all wired correctly following the existing pattern.
Cotabby/UI/Settings/Panes/GeneralPaneView.swift	Toggle and Binding added correctly; description text is accurate for the punctuation/whitespace suppression case.
Cotabby/UI/Settings/SettingsIndex.swift	New addSpaceAfterAccept case correctly categorised as .general, icon matches the toggle in GeneralPaneView, and search keywords are comprehensive.
CotabbyTests/SuggestionSessionReconcilerTests.swift	Six new unit tests cover: word suffix, digit suffix, punctuation endings, existing trailing whitespace, CJK/spaceless-script, and empty string — all meaningful branches of the new function.
Cotabby/Models/SuggestionEngineModels.swift	addSpaceAfterAccept field added to SuggestionSettingsSnapshot with a clear doc comment; struct remains Equatable and Sendable.
Cotabby/Models/SuggestionSettingsData.swift	addSpaceAfterAccept var added to SuggestionSettingsData with a clear doc comment explaining the opt-in default.
CotabbyTests/CotabbyTestFixtures.swift	Default parameter addSpaceAfterAccept: Bool = false added to the snapshot fixture factory, consistent with the production default.

Sequence Diagram

sequenceDiagram
    participant U as User (Tab key)
    participant SC as SuggestionCoordinator
    participant R as SuggestionSessionReconciler
    participant SI as SuggestionInserter
    participant S as ActiveSuggestionSession

    U->>SC: acceptSuggestion()
    SC->>R: insertionChunk(forAcceptedChunk:precedingText:)
    R-->>SC: insertionChunk (leading-space stripped if needed)
    SC->>S: advancing(by: acceptedChunk.count).isExhausted
    S-->>SC: isExhausted (exhaustion prediction)
    alt addSpaceAfterAccept ON AND session exhausted
        SC->>R: insertionChunkAppendingTrailingSpace(insertionChunk)
        R-->>SC: insertionText (+ trailing space if word char, non-CJK)
    else setting OFF or not exhausted
        SC-->>SC: "insertionText = insertionChunk"
    end
    SC->>SI: insert(insertionText)
    SI-->>SC: success / failure
    SC->>S: commitAcceptedChunk(acceptedChunk)
    alt exhausted
        S-->>SC: .exhausted
        SC->>SC: hideOverlay, armPostExhaustionAcceptance, schedulePrediction
    else advanced
        S-->>SC: .advanced(session)
        SC->>SC: presentAdvancedOverlay(insertionChunk)
    end

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_{Reviews (2): Last reviewed commit: "Merge remote-tracking branch 'origin/mai..." | Re-trigger Greptile}

[greptile-apps]

The description mentions punctuation and space as suppression cases but omits spaceless scripts (CJK, Thai, etc.). A user who writes in Japanese and enables this toggle will notice no space ever appears — the description as written doesn't tell them why. A small addition like "or in a language that doesn't use spaces (e.g. Chinese, Japanese)" would set the right expectation.

Suggested change

	description: "When accepting a suggestion finishes a word, also add a space so you can " +
	"keep typing. Skipped when it already ends in punctuation or a space.",
	description: "When accepting a suggestion finishes a word, also add a space so you can " +
	"keep typing. Skipped when it already ends in punctuation, a space, or a language " +
	"that doesn't use spaces (e.g. Chinese, Japanese).",

Note: If this suggestion doesn't match your team's coding style, reply to this and let me know. I'll remember it for next time!