#36347 node: don't abort on invalid -dbcache in settings.json

Removes the `noexcept` specifier from `LogOversizedDbCache` and adds functional test cases for integer and invalid non-integer `dbcache` values in `settings.json`. This allows parse exceptions from `GetIntArg` to propagate up to `AppInit`'s top-level exception handler, causing the node to exit with an informative error rather than aborting via `std::terminate`.

Problem: If `settings.json` contains a non-integer or out-of-range number for `dbcache` (such as `300.5`), `GetIntArg` throws `std::runtime_error`. Because `LogOversizedDbCache` was marked `noexcept`, this exception triggers `std::terminate` during startup instead of being handled by `AppInit`.

Evidence of importance:

• PR description and commit note uncaught exception crash during startup: 'libc++abi: terminating due to uncaught exception of type std::runtime_error: JSON integer out of range'
• The diff directly corroborates the mechanism: `LogOversizedDbCache` calls `CalculateDbCacheBytes` which calls `GetIntArg`, while the function was declared `noexcept`.

Risk of a mistake: low (tests). Only removes a noexcept specifier on an initialization logging helper to allow standard startup error handling to catch argument parse errors.

Changed since the previous assessment: The functional test in `feature_settings.py` was updated or rebased (testing both valid `300` and invalid `300.5` instead of `4096.5`).

Ready

Nothing known that would invalidate a review now.

Waiting on (from the thread read):

• nothing: no pending items or actions

Strong

substantive support, no open objection (8144225309)

Thread notes: Added re-ACK from 8144225309. Hamza1610 also re-ACKed, but without rationale and with no project contribution history, so it was not recorded as a support entry.

Objections, suggestions, and questions:

Support:

• 8144225309 (contributor) (ACK, 2026-10-05) [both: AppInit, settings.json]: On master a non-integer `dbcache` in settings.json aborts the node at startup. This change makes it exit with an error through `AppInit`, and the new test fails without it.
• 8144225309 (contributor) (ACK, 2026-11-01): (no reason given) [not substantive]

Participants:

• 8144225309 (contributor, support, 2 statements 2026-10-05 to 2026-11-01): ACKed with testing and explanation of startup behavior; re-ACKed commit 2e00693
• Hamza1610 (none, support, 4 statements 2026-10-07 to 2026-11-01): re-ACKed commit 2e00693; suggested adding a test for a valid integer dbcache value
• maflcko (member, neutral, 1 statements 2026-10-13 to 2026-10-13): asked if the PR can be closed due to CI failure or if the author is still working on it

12 lines under test/bench/ci.

• test/functional/feature_settings.py +12/-0
• src/node/caches.cpp +1/-1
• src/node/caches.h +1/-1

The short text the ranking pass compares across PRs.

Removes the noexcept specifier from LogOversizedDbCache so invalid dbcache values in settings.json produce a clean startup exit instead of a process abort. When settings.json contains a non-integer dbcache value, GetIntArg throws std::runtime_error, which hit the noexcept boundary and caused std::terminate to abort bitcoind during startup. Removing noexcept allows the exception to propagate to the AppInit handler, printing an informative error message and exiting with status 1.

P3 · bug fix

Fixes a startup crash caused by `std::terminate` when `settings.json` contains an invalid `dbcache`. Removing `noexcept` from `LogOversizedDbCache` allows the parse error to reach `AppInit`'s top-level exception handler and produce a clear error message instead of an abort.

Membership: Modifies configuration and startup error handling in `src/node/caches.cpp` when parsing settings from `settings.json`.

Factors: security/stability 1, bug 1, performance 0, user value 1, leverage 0