Replace ParseDate with unified Ragel -G2 scanner + recursive descent parser

Delete the 1650-line multi-pass constraint-satisfaction engine
(timeparser.cpp) and replace it with date_scan.rl: a Ragel -G2
scanner that tokenizes date strings into a flat token array, plus a
small recursive descent parser that dispatches on the leading token.

The scanner handles month names, day-of-week names, timezone
abbreviations, military timezone letters, meridian (AM/PM), ordinal
suffixes, and numbers — all as DFA alternations with no hash tables
or linear searches.

The parser dispatches on the first non-whitespace token:
  4+ digit number → ISO 8601 family (extended, basic, ordinal, week)
  Month name      → US order (Mmm DD [YYYY] HH:MM:SS / legacy)
  1-2 digit + Month → European order (DD Mmm YYYY HH:MM:SS)
  Day-of-week     → strip prefix, re-dispatch

This is a single code path — always exercised, always tested.  The
old architecture had two independent parsers (do_convtime + ParseDate)
where one could be broken without anyone noticing.

Sub-second precision: unified handling across all formats, accumulating
up to 7 fractional digits as hectonanoseconds (100ns), matching the
internal FACTOR_100NS_PER_SECOND resolution.

All 998 smoke tests pass.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

docs/design-date-parser.md

@@ -0,0 +1,282 @@
+# Design: Unified Date Parser
+
+## Status
+
+Proposed — replaces both `do_convtime()` and `ParseDate()` with a
+single Ragel -G2 scanner + recursive descent parser.
+
+## Background
+
+`convtime()` currently has two independent code paths:
+
+1. **`do_convtime()`** — Hand-written parser for the legacy format
+   `[Ddd] Mmm DD HH:MM:SS[.frac] YYYY`.  Works correctly.
+
+2. **`ParseDate()`** — 1650-line multi-pass constraint-satisfaction
+   engine.  Was completely broken from 2.13 through 2.14 due to a
+   `mux_min(int,int)` truncating `size_t`.  Nobody noticed for months.
+
+Having two parsers means two sub-second algorithms, two sets of
+validation rules, two things to maintain, and the ability for one to
+be broken without anyone knowing.  The fix is to make everything
+one thing.
+
+## Design Principle
+
+One parser, always used, always tested.  If it breaks, every
+`convsecs()`/`convtime()` round-trip fails and 900+ smoke tests
+scream.  No silent fallback to a different code path.
+
+## Architecture
+
+```
+convtime(input, [zone], [precision])
+  → date_parse(input) → FIELDEDTIME + zone info
+  → apply timezone logic
+  → return epoch string
+```
+
+`date_parse()` is the unified entry point.  It replaces both
+`lta.SetString()` (which called `do_convtime()`) and `ParseDate()`.
+
+### Ragel -G2 Scanner
+
+The scanner tokenizes the input into a flat array of typed tokens:
+
+```c
+enum DateToken {
+    TOK_EOF,
+    TOK_NUM,        // sequence of digits, value + digit count stored
+    TOK_MONTH,      // Jan..Dec / January..December → 1..12
+    TOK_DOW,        // Sun..Sat / Sunday..Saturday → 0..6
+    TOK_TZ_NAME,    // UTC, GMT, EST, PST, CST, MST, EDT, PDT, CDT, MDT,
+                    // HST, AKST, AKDT, BST, IST, CET, CEST, EET, EEST,
+                    // AEST, AST, ADT, UT → offset in minutes
+    TOK_TZ_MIL,    // A..Z (except J) → offset in minutes
+    TOK_MERIDIAN,   // AM=0, PM=12
+    TOK_SUFFIX,     // st, nd, rd, th
+    TOK_T,          // letter T (ISO separator)
+    TOK_W,          // letter W (ISO week prefix)
+    TOK_Z,          // letter Z (UTC indicator)
+    TOK_DASH,       // -
+    TOK_PLUS,       // +
+    TOK_COLON,      // :
+    TOK_DOT,        // .
+    TOK_COMMA,      // ,
+    TOK_SPACE,      // whitespace (collapsed)
+};
+```
+
+Ragel handles the name matching via DFA alternation.  Month names
+(24 alternations), day-of-week (14), timezone abbreviations (~25),
+and meridian (2) compile into a single goto-driven state machine.
+This is a jump table — faster than the old `ParseThreeLetters()`
+hash comparison or the `PD_TextTable` linear scan.
+
+Numbers carry their digit count, which the parser uses for
+disambiguation (1-2 digits = day/hour/minute/second, 3 digits =
+day-of-year, 4 digits = year, 5+ digits = extended year).
+
+### Recursive Descent Parser
+
+After scanning, the parser dispatches on the leading token(s):
+
+```
+parse_datetime(tokens):
+    skip optional TOK_DOW [TOK_COMMA] [TOK_SPACE]
+
+    if peek TOK_NUM(4+ digits) or TOK_PLUS or TOK_DASH(followed by digits(4+))
+        → parse_iso(tokens)
+
+    if peek TOK_MONTH
+        → parse_month_leading(tokens)
+
+    if peek TOK_NUM(1-2 digits) and peek+1 is TOK_MONTH
+        → parse_day_leading(tokens)
+
+    → fail
+```
+
+Each handler is a straight left-to-right walk consuming expected
+tokens.  No backtracking.
+
+#### parse_iso — ISO 8601 family
+
+```
+year = consume NUM(4+ digits)
+
+if peek TOK_W                          → ISO week date
+    consume W, NUM(2) week
+    optional DASH, NUM(1) day-of-week
+elif peek DASH + NUM(3)                → ISO ordinal
+    consume DASH, NUM(3) day-of-year
+elif peek DASH + NUM(1-2)              → ISO extended
+    consume DASH, NUM(1-2) month, DASH, NUM(1-2) day
+elif peek NUM(4) (MMDD compact)        → ISO basic
+    split NUM into month(2) + day(2)
+elif peek NUM(3) (DDD compact)         → ISO basic ordinal
+    day-of-year = NUM
+
+parse_time_part(tokens)                 (see below)
+```
+
+#### parse_month_leading — Mmm DD[,] YYYY time [TZ]
+
+```
+month = consume TOK_MONTH
+day   = consume NUM(1-2)
+optional TOK_SUFFIX, TOK_COMMA
+optional TOK_SPACE
+year  = consume NUM (any digit count for year)
+parse_time_part(tokens)
+```
+
+This covers:
+- `Jan 01 00:00:00 2000` (after time, year — legacy order variant)
+- `January 1st, 2026 10:43:00 UTC`
+- `Apr 6 2026 10:43:00 EST`
+
+Note: The legacy `do_convtime()` format puts time before year:
+`Mmm DD HH:MM:SS YYYY`.  The unified parser needs to handle both
+orders.  After consuming month and day, if the next token looks like
+a time (NUM:NUM), parse time then year.  If it looks like a year
+(4-digit NUM), parse year then time.
+
+```
+if peek NUM + TOK_COLON               → time first, then year
+    parse_time_part(tokens)
+    year = consume NUM
+else
+    year = consume NUM
+    parse_time_part(tokens)
+```
+
+#### parse_day_leading — DD Mmm YYYY time [TZ]
+
+```
+day   = consume NUM(1-2)
+optional TOK_SUFFIX
+month = consume TOK_MONTH
+optional TOK_COMMA
+year  = consume NUM
+parse_time_part(tokens)
+```
+
+#### parse_time_part — HH:MM:SS[.frac] [TZ]
+
+```
+optional TOK_T or TOK_SPACE (separator)
+hour   = consume NUM(1-2)
+consume TOK_COLON
+minute = consume NUM(2)
+optional:
+    consume TOK_COLON
+    second = consume NUM(2)
+    optional:
+        consume TOK_DOT
+        frac = consume NUM (1-9 digits, right-pad to 7 with zeros)
+optional TOK_MERIDIAN (adjust hour: 12→0, add PM offset)
+parse_timezone(tokens)
+```
+
+#### parse_timezone
+
+```
+if peek TOK_Z                          → UTC (offset = 0)
+if peek TOK_TZ_NAME                    → named offset
+if peek TOK_TZ_MIL                     → military offset
+if peek TOK_PLUS or TOK_DASH           → numeric offset
+    sign = consume
+    offset = consume NUM(4) as HHMM, or NUM(2) HH + COLON + NUM(2) MM
+else                                   → no timezone specified
+```
+
+## Sub-second Handling
+
+Unified across all formats.  After the seconds, if a `.` follows:
+
+1. Consume up to 9 digits.
+2. Right-pad with zeros to exactly 7 digits.
+3. Store as hectonanoseconds (100ns units).
+4. Split into milliseconds (digits 1-3), microseconds (4-6),
+   nanoseconds (7, ×100) for FIELDEDTIME.
+
+This replaces both `ParseDecimalSeconds()` in `do_convtime()` and
+the broken inline parser in the old `PD_GetFields()`.
+
+## Supported Formats
+
+### ISO 8601
+
+```
+2026-04-06T10:43:00Z
+2026-04-06T10:43:00+0000
+2026-04-06T10:43:00-07:00
+2026-04-06T10:43:00.1234567Z
+2026-04-06 10:43:00 UTC
+20260406T104300Z
+2026-096T10:43:00Z
+2026W15-1T10:43:00Z
+2026-04-06
+-1605-120T12:34:56Z
+```
+
+### Legacy / Name-based
+
+```
+Jan 01 00:00:00 2000                     convsecs() output
+Wed Jun 24 10:22:54 1992                 with day-of-week
+Jun 24 10:22:54.123456 1992              with sub-seconds
+April 6, 2026 10:43:00 UTC              full month, comma
+Apr 6 2026 10:43:00 EST                 year before time
+January 1st 2000 00:00:00 Z             ordinal suffix
+6 Apr 2026 10:43:00 GMT                 European order
+Mon, 6 Apr 2026 10:43:00 +0000          RFC 2822-like
+Apr 6 2026 10:43:00pm Z                 AM/PM
+```
+
+### Explicitly Not Supported
+
+```
+04/06/2026        ambiguous (MM/DD vs DD/MM)
+6.4.2026          ambiguous (DD.MM vs MM.DD)
+Apr 6 26          ambiguous (year 26 vs day 26?)
+```
+
+## File Layout
+
+```
+mux/lib/date_scan.rl       Ragel source (scanner)
+mux/lib/date_scan.cpp       Generated (read-only, chmod a-w)
+mux/lib/date_parse.cpp      Recursive descent parser
+mux/lib/timeparser.cpp       Deleted
+mux/lib/timeutil.cpp         do_convtime() removed
+mux/include/timeutil.h       ParseDate() signature unchanged or
+                              replaced by date_parse()
+```
+
+Alternatively, the parser can live in the same `.rl` file after
+the `%%write` block, keeping scanner and parser together.
+
+## Testing
+
+- `testcases/convtime_fn.mux` — legacy format tests (must still pass)
+- `testcases/parsedate_fn.mux` — update with ISO + name-based tests
+- All 998+ smoke tests must continue to pass
+- The round-trip `convtime(convsecs(N, utc), utc) == N` must hold
+  for all valid N
+
+## Migration
+
+1. Write `date_scan.rl` (scanner) and parser.
+2. Wire as the sole implementation of date parsing.
+3. Remove `do_convtime()` and old `ParseDate()`.
+4. Verify all smoke tests pass.
+5. Update `help convtime` examples.
+
+## Size Estimate
+
+- Ragel scanner: ~150 lines of `.rl` (names are just alternations)
+- Recursive descent parser: ~200 lines of C++
+- Total: ~350 lines replacing ~1850 lines
+  (`do_convtime` ~130 + `ParseDate` ~1650 + helpers)

docs/generated-files.md

@@ -13,6 +13,7 @@ Do not hand-edit generated files in this repository. Edit the source input and r
 | `mux/modules/engine/art_scan.cpp` | `mux/modules/engine/art_scan.rl` | `ragel -G2` |
 | `mux/modules/engine/ast_scan.cpp` | `mux/modules/engine/ast_scan.rl` | `ragel -G2` |
 | `mux/lib/color_ops.c` | `mux/lib/color_ops.rl` | `ragel -G2 -C` |
+| `mux/lib/date_scan.cpp` | `mux/lib/date_scan.rl` | `ragel -G2` |
 | `mux/muxescape/muxescape.cpp` | `mux/muxescape/muxescape.rl` | `ragel -G2` |
 | `mux/include/utf8tables.h` | Unicode inputs under `utf/` | `utf/` pipeline / `make` |
 | `mux/lib/utf8tables.cpp` | Unicode inputs under `utf/` | `utf/` pipeline / `make` |

mux/lib/Makefile.am

@@ -12,7 +12,7 @@ AM_CFLAGS = -O2 -Wall -Wextra -Wno-implicit-fallthrough -std=c11
 
 LIBMUX_SRC = libmux.cpp \
     sha1.cpp svdrand.cpp svdhash.cpp \
-    timeutil.cpp timeabsolute.cpp timedelta.cpp timeparser.cpp timezone.cpp \
+    timeutil.cpp timeabsolute.cpp timedelta.cpp date_scan.cpp timezone.cpp \
     utf8_collate.cpp utf8_grapheme.cpp utf8_normalize.cpp utf8tables.cpp \
     strtod.cpp alarm.cpp mathutil.cpp stringutil.cpp alloc.cpp dbutil.cpp
 

mux/lib/Makefile.in

@@ -269,7 +269,7 @@ AM_CPPFLAGS = -I$(top_srcdir)/include -I$(top_srcdir)/ganl/include -I$(top_srcdi
 AM_CFLAGS = -O2 -Wall -Wextra -Wno-implicit-fallthrough -std=c11
 LIBMUX_SRC = libmux.cpp \
     sha1.cpp svdrand.cpp svdhash.cpp \
-    timeutil.cpp timeabsolute.cpp timedelta.cpp timeparser.cpp timezone.cpp \
+    timeutil.cpp timeabsolute.cpp timedelta.cpp date_scan.cpp timezone.cpp \
     utf8_collate.cpp utf8_grapheme.cpp utf8_normalize.cpp utf8tables.cpp \
     strtod.cpp alarm.cpp mathutil.cpp stringutil.cpp alloc.cpp dbutil.cpp
 
@@ -488,13 +488,17 @@ all-local: libmux.so
 -include $(LIBMUX_CXX_OBJS:.lo=.d)
 -include $(LIBMUX_C_OBJS:.lo=.d)
 
-# Ragel .rl -> .c
-# Ragel .rl -> .c — output is read-only to prevent accidental edits.
+# Ragel .rl -> .c/.cpp — output is read-only to prevent accidental edits.
 color_ops.c: color_ops.rl $(top_srcdir)/include/color_ops.h
 	chmod u+w $@ 2>/dev/null || true
 	ragel -G2 -C -o $@ $<
 	chmod a-w $@
 
+date_scan.cpp: date_scan.rl $(top_srcdir)/include/timeutil.h
+	chmod u+w $@ 2>/dev/null || true
+	ragel -G2 -o $@ $<
+	chmod a-w $@
+
 libmux.so: $(LIBMUX_OBJS)
 	$(CXX) $(CXXFLAGS) $(DYNAMICLIB_CXXFLAGS) -Wl,-soname,libmux.so -o $@ $(LIBMUX_OBJS) $(LIBS) $(DL_LIB) $(SQL_LIBS)