[prince-0408]

Description

This PR resolves #598 ("Conjugate command returns 'Not in Wikidata' for valid verbs") and #738 ("Redundant sequential SQLite file opens and identical SELECT queries").

Root Causes

1. Missing Database Fallback in DatabaseFileManager: When keyboard users download their language packages, the data is saved in ${language}LanguageData.sqlite (which includes the verbs table). However, ConjugateDataManager exclusively queried getConjugateDatabase(), which looked only for ${language}ConjugateData.sqlite (downloaded only in the Conjugate standalone app). Since the file didn't exist for keyboard users, getConjugateDatabase() returned null, failing all valid verbs with "Not in Wikidata".
2. Strict Single-Column & Case-Sensitive Matching: getVerbCursor() used WHERE $columnName = ? on only the infinitive column. Any uppercase or mixed-case verb (e.g. German capitalized forms, or uppercase typing), inflected verb form (e.g. typing "went" or "running"), or verbs with common grammatical prefixes ("to ", "se ", "sich ", "s'") immediately failed.
3. Severe N+1 Disk I/O & Connection Leaks: getTheConjugateLabels looped across every single tense and form (up to 120 iterations per verb), opening and closing the database file sequentially on every call. Additionally, parseComplexForm invoked getConjugateDatabase() without closing the database connection.

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Key Changes

• Database Fallback & Case Normalization (DatabaseFileManager.kt):
  • Added an automatic fallback to getLanguageDatabase() when ${language}ConjugateData.sqlite is absent.
  • Normalized database filenames with .uppercase() to prevent filesystem casing mismatches on Linux/Android ext4 filesystems.
• Single-Query Caching & Fallback Lookup Ladder (ConjugateDataManager.kt):
  • Opens the database connection once per lookup and caches the verb row into an in-memory map.
  • Queries candidate infinitive columns using case-insensitive SQL matching: LOWER(${SqlIdentifier.quote(col)}) = LOWER(?).
  • Supports prefix-stripping fallback for leading "to ", "se ", "sich ", and "s'".
  • Adds an inflected form fallback that searches verbs table columns if direct infinitive matching yields no results.
  • Reuses the existing open database connection in auxiliary parsing (parseComplexFormFromRow), eliminating database connection leaks.
  • Added getStructuredConjugations() to efficiently serve UI screens.
• SQL Sanitization & Table Column Discovery (SQLiteExtensions.kt):
  • Added getTableColumns() helper with SqlIdentifier validation and quoting.
• UI State Preservation & Fast Loading (ConjugationSelectionScreen.kt):
  • Uses manager.getStructuredConjugations() to load forms in a single pass.
  • Uses rememberSaveable for selectedTenseGroup to survive device rotations and fold/unfold events.
• Unit Testing (ConjugateDataManagerTest.kt):
  • Added comprehensive JUnit 5 tests covering exact infinitive lookups, case-insensitivity (HABEN -> haben), prefix-stripping (to walk -> walk), inflected form lookups (went -> go), and missing database handling.
• Changelog:
  • Updated CHANGELOG.md under Bug Fixes.

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Closes #598
Closes #738

[Roniscend]

When a verb column is missing the complex form parsing now returns just the auxiliary, like have instead of an empty string which would show wrong conjugations. The new fallback also changes what the Conjugate app search returns and the tests only use mocks so they never check the SQL or the actual fix.

[prince-0408]

Thanks for the review @Roniscend! Addressed in the latest commit!

[andrewtavis]

@ashb155, can you also take a look at this to see if it addresses #738?

[ashb155]

yes it does, looks good to me @andrewtavis !

[andrewtavis]

Thanks, @ashb155! I'll look into scribe-org/Scribe-Data#725 and then we can redeploy Scribe-Server and finalize this one. @angrezichatterbox, would be good for you to also take a look once the Scribe-Data/Scribe-Server processes are finalized :)