fix: preserve download integrity and progress across transfers

[linroid]

HTTP downloads could accept incorrect range responses, lose final segment progress, miss live connection changes, or report an empty download as complete without creating or truncating its destination. This change fixes those cases and adds regression coverage through real Ktor connections and SQLite task storage.

• Validate range responses and body lengths before allowing out-of-range writes; preserve single-transfer downloads from servers without range support.
• Preserve segment checkpoints on cancellation/failure, retain completed progress, and restart transfers when the connection count changes.
• Apply retry handling to initial metadata resolution and keep paused progress consistent with saved segments.
• Create/truncate zero-byte destinations and correctly decode UTF-8 filenames from URLs and Content-Disposition headers.
• Add deterministic local HTTP integration tests for interruption, retries, cancellation, resume, SQLite restart, and file integrity. Public HTTPS tests verify GitHub content by SHA-256 and HTTPBingo range downloads byte-for-byte; they are excluded from ordinary test runs.

Validation passed on this branch: 605 tests reported with zero failures (Gradle reused matching cached results where applicable), including freshly executed public HTTPS tests. Desktop and Android compilation also passed.

./gradlew :library:api:jvmTest :library:core:jvmTest :library:ktor:jvmTest \
  :library:ftp:jvmTest :library:remote:jvmTest :library:server:test \
  :app:shared:jvmTest :app:desktop:compileKotlin :library:core:compileAndroidMain \
  -PpublicDownloadTests=true

Public tests require internet access and fail on service outages rather than silently skipping. Android validation is compilation only; the file-accessor change has not been exercised on an Android device.

[chatgpt-codex-connector]

Codex Review Summary

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Review	Status	Commit	Review trigger
📝 Code Review	✅ Completed 2026-09-21T14:42:30.355050Z	67fa565	PR opened

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[chatgpt-codex-connector]

💡 Codex Review

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Reviewed commit: 67fa56568a

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[chatgpt-codex-connector]

Accept chunked full responses when Range is ignored

When the HEAD response supplies a size but the subsequent GET ignores Range: bytes=0-(N-1) and returns the full body using chunked transfer encoding, response.contentLength() is null, so this branch rejects the response before reading it. Ignoring a Range request and omitting Content-Length are both valid server behaviors, and the body loop can still validate the received byte count against the range-derived expectedBytes; as written, downloads from such no-range servers now fail with KetchError.Unsupported.

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[github-actions]

Test Results

  821 files  + 7    821 suites  +7   5m 11s ⏱️ -19s
3 542 tests +66  3 542 ✅ +66  0 💤 ±0  0 ❌ ±0 
4 820 runs  +66  4 820 ✅ +66  0 💤 ±0  0 ❌ ±0 

Results for commit 67fa565. ± Comparison against base commit 48ed5c6.

This pull request removes 1 and adds 67 tests. Note that renamed tests count towards both.

com.linroid.ketch.file.PathFileAccessorPreallocateTest ‑ preallocate_zero_isNoOp[jvm]

com.linroid.ketch.engine.HttpDownloadIntegrationTest ‑ cancel_activeTransfer_cleansUpPartialFile[jvm]
com.linroid.ketch.engine.HttpDownloadIntegrationTest ‑ download_edgeSizes_preservesEveryByte[jvm]
com.linroid.ketch.engine.HttpDownloadIntegrationTest ‑ download_emptyFile_replacesExistingExplicitDestination[jvm]
com.linroid.ketch.engine.HttpDownloadIntegrationTest ‑ download_extendedServerFilename_usesDecodedName[jvm]
com.linroid.ketch.engine.HttpDownloadIntegrationTest ‑ download_ignoredRange_failsInsteadOfCorruptingFile[jvm]
com.linroid.ketch.engine.HttpDownloadIntegrationTest ‑ download_interruptedBody_retriesFromWrittenOffset[jvm]
com.linroid.ketch.engine.HttpDownloadIntegrationTest ‑ download_missingResource_failsWithoutRetryOrOutputFile[jvm]
com.linroid.ketch.engine.HttpDownloadIntegrationTest ‑ download_noRangeSupport_usesSingleCompleteTransfer[jvm]
com.linroid.ketch.engine.HttpDownloadIntegrationTest ‑ download_transientHeadFailure_retriesProbe[jvm]
com.linroid.ketch.engine.HttpDownloadIntegrationTest ‑ download_transientServerError_retriesSuccessfully[jvm]
…