Model card: restore full README from GitHub, add commercial license option

README.md

@@ -13,3 +13,121 @@ tags:
 
 > Mirrored from [https://github.com/SNAPKITTYWEST/snapkitty-regex](https://github.com/SNAPKITTYWEST/snapkitty-regex) at commit `b14a2eb`. Part of the **SnapKitty October 2026 main drop**.
 
+# snapkitty-regex
+
+A Thompson NFA regular expression engine in C — under 700 lines, zero
+dependencies, no exponential backtracking, ever.
+
+Built as an exercise from the guides in
+[AHMADALIPARR/build-your-own-x](https://github.com/AHMADALIPARR/build-your-own-x)
+("Build your own `Regex Engine`"), primarily Russ Cox's
+*[Regular Expression Matching Can Be Simple And Fast](https://swtch.com/~rsc/regexp/regexp1.html)*.
+
+## The idea
+
+Most popular regex engines (Perl, Python, Ruby, Java, PCRE) simulate an
+NFA by *backtracking*: guess a path, and retry on failure. On patterns
+like `a?a?a?aaa` that means trying all 2^n combinations — Perl needs
+**60+ seconds** to match a 29-character string.
+
+This engine instead simulates *all* NFA paths in parallel, tracking the
+set of reachable states one input character at a time (Thompson's 1968
+algorithm). Matching is **O(m·n)** worst case for pattern length m and
+text length n. There are no pathological inputs.
+
+```
+infix pattern --re2post--> postfix --post2nfa--> NFA --pump--> match?
+                  (explicit '.' concat)   (Thompson construction)
+```
+
+## Syntax
+
+| construct | meaning |
+|---|---|
+| `abc` | literal characters match themselves |
+| `e1 e2` | concatenation |
+| `e1\|e2` | alternation |
+| `e*` | zero or more |
+| `e+` | one or more |
+| `e?` | zero or one |
+| `(e)` | grouping |
+| `\` + metachar | literal metacharacter: `\* \+ \? \| \( \) \\` |
+| `.` | literal dot (no wildcard — see roadmap) |
+
+Precedence: `|` weakest, then concatenation, then `* + ?`. Matching is
+byte-oriented.
+
+## Build & test
+
+```sh
+make          # builds ./regex, clean compile, zero warnings
+make test     # 82-check correctness harness (fullmatch, search, bad patterns)
+make bench    # pathological benchmark vs Python's re
+```
+
+## Usage
+
+```sh
+$ ./regex 'a(bb)+a' abbbba abba abbba
+abbbba: MATCH
+abba: MATCH
+abbba: NO MATCH
+
+$ ./regex -s 'colou?r' 'the colour blue'
+the colour blue: MATCH
+```
+
+Exit codes: `0` all matched, `1` some didn't, `2` usage/bad pattern.
+
+As a library (`src/regex.h`):
+
+```c
+Regex *re = re_compile("(ab|cd)+e");
+int m = re_fullmatch(re, "cdabe");  /* whole string */
+int p = re_match(re, "cdabex");     /* prefix of string */
+int s = re_search(re, "xxcdabexx"); /* anywhere in string */
+re_free(re);
+```
+
+## Benchmark
+
+`a?`^n`a`^n against `a`^n — the article's pathological case:
+
+| n | snapkitty-regex | python `re` |
+|---|---|---|
+| 10 | 0.0011s | 0.0000s |
+| 20 | 0.0010s | 0.0442s |
+| 24 | 0.0013s | 0.7139s |
+| 26 | 0.0014s | 3.0580s |
+| 500 | 0.0021s | (heat death of universe) |
+
+(The ~1ms floor on our side is process-spawn overhead, not matching.)
+
+## What's hardened vs the article's reference code
+
+- **No fixed static buffers** — postfix output and the paren stack are
+  sized from the input instead of `char buf[8000]` / `paren[100]`.
+- **Backslash escapes** for metacharacters.
+- **Literal dots** — a `.` in the pattern can't collide with the postfix
+  concatenation operator anymore (this crashes the original).
+- **Real error paths** — malformed patterns and `malloc` failures return
+  `NULL` instead of crashing; partial allocations unwind cleanly.
+- **Reusable, releasable** — compiled patterns are opaque `Regex*`
+  values with `re_free`; the accept state and dedup generation are
+  per-pattern, not globals.
+- **Prefix match + search** on top of full match.
+
+## Roadmap
+
+- `.` wildcard / character classes `[a-z]`
+- Capture groups and submatch extraction
+- DFA / hybrid execution for very large inputs
+- Streaming matcher API
+
+---
+
+### 💼 Commercial License
+
+SnapKitty code is free and open under **AGPL-3.0** for open-source use. Building a commercial product or service? A **proprietary commercial license** from Snapkitty Collective LLC lets you ship this code without the AGPL's source-sharing and network-use obligations.
+
+**[→ Get a commercial license](mailto:A.parr@belespritdaccord.uk?subject=Commercial%20license:%20snapkitty-regex)** · A.parr@belespritdaccord.uk