nx_linemap.nx

nx_linemap.nx -- OUT-OF-BAND expanded-line -> (file, source-line) map. WHY THIS EXISTS nx_cc compiles PRE-EXPANDED source: nx_import.nx splices every imported file inline into ONE flat buffer, so every line number the lexer produces is a line in that flat stream. Consequences, both measured: * a diagnostic can say WHERE the compiler was but never WHICH FILE the author must open (nx_parse.nx says so in-source: "Mapping back to per-file lines is a separate rung"; the /compare/lang matrix scores the 5W+H voice 24/25 and names the missing point as the file name); * nx_dwarf_line.nx -- a complete DWARF v5 .debug_line builder -- has no file table to emit, so it sits built and unwired along with 11 sibling organs. This module is the substrate both of those need. It is NOT itself the fix to either; it is the thing they were both missing. DESIGN DECISION -- a SPAN TABLE, not C's `#line` directives The C toolchain solves this IN BAND: cpp injects `#line N "file"` into the expanded text and the compiler's lexer understands them. We reject that, and the reasons are worth stating because the in-band design is the older and more familiar one: 1. EVERY consumer of the expanded buffer must then understand a second syntax that is not NishiLang -- the lexer, and anything that ever reads the buffer for any other purpose. One producer's convenience becomes every reader's obligation. 2. It is FORGEABLE FROM ORDINARY SOURCE. The expanded buffer carries string literals verbatim; a literal containing a newline followed by `#line 1 "victim.nx"` would relabel the real code after it. Diagnostics -- and later, debug info a debugger trusts -- could be made to point at an innocent file BY WRITING A STRING. Putting metadata in a channel that also carries attacker-writable text is a confusion of layers, and the estate has already paid for that class once (the in-STRING `}` that closed a brace skip mid-body, nx_import.nx skip_func_main, debt 1785894599). 3. It perturbs the very bytes nx_diag_caret prints, so the snippet machinery would have to learn to skip directives to avoid showing them to the author. Clang (SourceManager) and rustc (SourceMap) both keep this mapping OUT of the text, beside it. We match that known good. THE COST WE ACCEPT, STATED PLAINLY: an out-of-band map is a parallel structure that can DESYNC from the buffer it describes -- it is only as true as its producer. In-band directives cannot desync, because they ARE the buffer. That is