chore: Added notes about how to evaluate binary size.

AUDITING_BINARY_SIZE.md

@@ -0,0 +1,96 @@
+# Visualizing & Managing `thor` Binary Size
+
+How to inspect what makes up the compiled `thor` binary, and how to keep that
+inspection useful once we bundle layout/asset files into the binary.
+
+## Quick inspection (tools already available)
+
+The binary is a not-stripped ELF, so it ships symbols we can break down.
+
+```bash
+# Section totals (text / data / bss)
+size ./thor
+
+# Top symbols by size
+nm --print-size --size-sort --radix=d ./thor \
+  | awk '{sz=$2+0; sub(/^[0-9a-fA-F]+ +[0-9]+ +[A-Za-z] +/,""); printf "%8d  %s\n", sz, $0}' \
+  | sort -rn | head -25
+
+# Aggregate symbol sizes by Odin module namespace (foo::bar -> "foo")
+nm --print-size --size-sort --radix=d ./thor \
+  | awk '{sz=$2+0; rest=$0; sub(/^[0-9a-fA-F]+ +[0-9]+ +[A-Za-z] +/,"",rest);
+          ns=rest; if (rest ~ /::/){sub(/::.*/,"",ns)}
+          else if (rest ~ /^ts_/){ns="treesitter (ts_*)"} else {ns="<other/runtime>"};
+          s[ns]+=sz} END{for (k in s) printf "%9d  %s\n", s[k], k}' \
+  | sort -rn | head -25
+```
+
+As of this writing the top contributors were: tree-sitter tables (~118 KB),
+`main` (~96 KB), runtime/other (~93 KB), `mustache` (~67 KB), then `fmt` /
+`encoding_json` from the stdlib.
+
+## Better visualization: `bloaty`
+
+`bloaty` (Google's binary-size profiler) is the right tool. Not installed, but
+runnable via Nix:
+
+```bash
+bloaty ./thor                      # by section
+bloaty ./thor -d symbols -n 30     # by symbol, hierarchical
+bloaty ./thor -d sections,symbols  # section then symbols within each
+# via nix (no install):
+nix run nixpkgs#bloaty -- ./thor -d symbols -n 30
+```
+
+For a stripped-size estimate:
+
+```bash
+readelf -S ./thor | grep -E 'debug|symtab|strtab'   # strippable overhead
+strip -s ./thor -o thor.stripped && size thor.stripped
+```
+
+Odin also supports smaller builds: `odin build . -o:size -no-bounds-check`.
+
+## IMPORTANT: keeping bloaty useful once we bundle layouts into the binary
+
+Today the VFS (`vfs.odin`) reads layout/asset files lazily from disk at runtime
+(`VFS_Entry.fs_path` + `os.read_entire_file_from_path`); `VFS_Entry.data` is
+never populated at build time. So embedded content is **not** in `./thor` yet.
+
+When we switch to embedding via Odin `#load(...)`, the file bytes land in the
+binary's `.rodata` section. Whether bloaty can show *per-file* sizes depends on
+how we emit the embed:
+
+- **Section total — always visible.** `.rodata` grows by ~the total bundled
+  size. `bloaty ./thor -d sections` (or `size`) shows the aggregate, and we can
+  diff before/after. This always works.
+
+- **Per-file breakdown — only if each file is a NAMED symbol.**
+  - A generated `map[string]VFS_Entry` literal full of inline `#load(...)`
+    expressions makes each blob an **anonymous** `.rodata` constant. Bloaty
+    lumps them together — no per-file breakdown.
+  - Assigning each file to its own **package-level variable** makes each a named
+    global symbol, so `bloaty ./thor -d symbols` (and the `nm` recipe above)
+    show each file individually:
+
+    ```odin
+    layout_base_html   := #load("defaults/layouts/base.html")
+    layout_single_html := #load("defaults/layouts/single.html")
+    // ...then reference these in the VFS map instead of inlining #load.
+    ```
+
+### Decision to bake into the bundling codegen
+
+When we build the codegen that replaces the runtime `mount_dir` disk walk, have
+it emit **one named package-level variable per embedded file** (not an anonymous
+map literal). That single choice is what makes bloaty / `nm` per-file analysis
+possible — cheap to do up front, painful to retrofit.
+
+Additional options that help regardless of symbolization:
+
+1. Build with Odin `-debug` (DWARF) and use `bloaty ./thor -d compileunits` to
+   attribute embedded bytes to the generated source file.
+2. Since the generator already knows every file and its size, emit a size
+   manifest at bundle time (`path -> bytes`, sorted / treemap). This is the most
+   reliable per-file view and can't drift from reality; bloaty then just
+   confirms the `.rodata` total matches.