I updated from ^4.5.5-b to ^4.5.5-c since ^4.5.5-b is not "patchable" (see here).

This is explicit requirement from SQLite Session Extension docs

I found that when we #include <sqlite3.h> XCode links it to sqlite3.h header provided by the system. Unfortunately this header doesn't provide type and function definitions necessary for sqlite session extension. It is clearly a mistake made by Apple since they claim that every iOS version since 11.0 uses sqlite version greater than or equal to 3.19.3 whereas sqlite session extension is available since sqlite version 3.13.0.

XCode uses system provided headers as a last resort so we can make it use header from amalgamation if we include path to it in HEADER_SEARCH_PATHS.

Actually this change is not necessary. According to docs it enables XCode to create mapping from header filename to header file path without using HEADER_SEARCH_PATH. But in our case we use HEADER_SEARCH_PATH to link against correct sqlite3.h so this change is not necessary. I tested that code (entire stack not just this diff) compiles and works if it is removed.

Actually after some research I think we don't have to. According to CocoaPods docs the compiler_flags property of podspec tells the XCode to set those flags when compiling the particular pod files. According to apple docs setting OTHER_CFLAGS in this podspec sets those flags globally for all C, C++, Obj-C++ files. I don't think it has ever been an issue - it was just unnecessary. I tested the entire stack after removing OTHER_CFLAGS entry.