Greptile Summary

This PR consolidates the dual RuntimeConfig structs (one in internal/config, one in internal/engine/types) into a single types.RuntimeConfig, renames MaxConnectionsPerHost → MaxConnectionsPerDownload throughout the codebase, and introduces DefaultRuntimeConfig() so callers no longer create sparse struct literals that silently disable health-check features.

• Field rename & constant adjustment: MaxConnectionsPerHost → MaxConnectionsPerDownload across 29 files; getter fallback constant changed from PerHostMax = 64 to PerDownloadMax = 32; a deprecated MaxConnectionsPerHost alias (tagged json:\"-\") is retained in NetworkSettings for backward compatibility.
• Getter semantics: Health-check fields (StallTimeout, SlowWorkerThreshold, SlowWorkerGracePeriod, SpeedEmaAlpha) now treat zero as "opt-out" rather than falling back to the package default, backed by matching guards in health.go and worker.go. Download() and both downloader constructors now use DefaultRuntimeConfig() to fix the stall/slow-worker regression.
• Bitmap normalisation: RestoreBitmap now allocates a correctly-sized bitmap and copies into it, preventing a panic when a persisted bitmap is shorter than expected.

Confidence Score: 5/5

Safe to merge; all production paths now use DefaultRuntimeConfig() so health checks remain active, and bitmap normalisation prevents resume-time panics.

The core fixes are correct and well-tested. Two undocumented constant changes (SlowWorkerThreshold 0.50→0.30 and StallTimeout 5s→3s) alter engine behaviour for all default-settings users, and a minor getter asymmetry means MaxTaskRetries=0 cannot disable retries while its sibling fields can be zeroed to opt out.

internal/engine/types/config.go — the constant and getter-semantics changes are the most impactful and least documented part of this PR.

Important Files Changed

Fix the following 2 code review issues. Work through them one at a time, proposing concise fixes.

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### Issue 1 of 2
internal/engine/types/config.go:41-44
**Silent behavioral changes to default health-check constants**

`SlowWorkerThreshold` dropped from `0.50` to `0.30`, and `StallTimeout` dropped from `5s` to `3s`. For users relying on engine defaults (i.e. not configuring these in settings), the slow-worker cancellation threshold is now 30 % of mean speed instead of 50 %, making it considerably less aggressive. Stall detection also fires sooner (3 s vs 5 s). These are meaningful behavioral differences that aren't captured in the PR description, making them easy to overlook in production if users report changed download behaviour.

Also note: the renamed constant `PerDownloadMax = 32` (was `PerHostMax = 64`) halves the getter fallback for connections. All known production paths now call `DefaultRuntimeConfig()` which explicitly sets 32, so this only matters for partial struct literals—but the change is worth documenting.

### Issue 2 of 2
internal/engine/types/config.go:120-125
**`GetMaxTaskRetries` asymmetry with opt-out siblings**

The struct comment documents two groups: capacity-style settings (zero → use default) and opt-out settings (zero → disable). `GetMaxTaskRetries` uses `<= 0` as the fallback, which is correct for a capacity-style field, but that means `MaxTaskRetries = 0` cannot be used to disable retries entirely. `StallTimeout`, `SlowWorkerThreshold`, `SlowWorkerGracePeriod`, and `SpeedEmaAlpha` all allow 0 to opt out. If a future caller wants zero retries (e.g. a probe-only path), they have no way to express that. A comment on the getter clarifying this constraint would close the ambiguity.

_{Reviews (2): Last reviewed commit: "fix: Fixed sparse runtime configs" | Re-trigger Greptile}