F3.2: std.cli minimal subcommand + flag parser over explicit []string

Extend std/cli.sx with a zero-heap argument parser that the caller drives
over a logical argv ([]string), separate from the F3.1 os_args accessor.

Grammar: <group> <command> [--flag VALUE | --bool]... [--json] [-- rest...]
  - (group, command) dispatched against a caller-provided Command table;
    no match -> error.UnknownCommand.
  - value-taking vs boolean flags fixed by each command's FlagSpec list;
    --json is a reserved global boolean surfaced as parsed.json.
  - `--` or the first bare operand ends flag parsing; the remainder is
    parsed.rest (operand views).

Heap discipline (heap-discipline.md): zero heap, zero copy. group/command/
flag values/rest are all VIEWS into args. Parsed is a by-value stack struct;
flag presence/values live in a fixed [16]FlagValue inline array indexed by
spec position (no per-flag allocation, no context.allocator). The flag-spec
list and command table are caller storage passed as views.

Failure surfacing (no silent skip): unknown command, unknown flag, a
value-flag missing its value, and an absent required flag each raise a
specific CliError variant; a caller-owned Diag records the offending token
(index + view) before each raise, since error tags carry no data.

examples/0717 drives the parser over explicit []string vectors: a valid
group/command/--flag/--bool/--json case (asserting parsed values + that
values are views into argv), subcommand dispatch, `--`/bare-operand
separators, and the five failure variants each asserted via destructure +
Diag. zig build && zig build test && run_examples.sh green (385 passed).

examples/0717-modules-cli-parse.sx

@@ -0,0 +1,137 @@
+// CLI argument PARSER from `modules/std/cli.sx` (F3.2) — subcommand
+// dispatch + `--flag` parsing over an EXPLICIT logical argv (`[]string`).
+//
+// Every argv vector below is an explicit `[]string` literal (the caller's
+// logical args, program name already removed). The suite proves:
+//
+//   1. DISPATCH    — `<group> <command>` selects the right command in the
+//                    caller's table; group/command are VIEWS into argv.
+//   2. FLAGS       — `--out VALUE` (value-taking) binds a VIEW of the next
+//                    token; `--verbose` (boolean) records presence; the
+//                    reserved `--json` mode flag surfaces as `parsed.json`.
+//   3. SEPARATORS  — `--` and the first bare operand both stop flag
+//                    parsing; the remainder is `parsed.rest` (operand VIEWS).
+//   4. HEAP        — flag values / group / command / rest all point INSIDE
+//                    the input argv (zero copy); `Parsed` is a stack value.
+//   5. FAILURES    — unknown command, unknown flag, missing required flag,
+//                    and a value-flag with no value each raise the specific
+//                    `CliError` variant on the error channel, and the
+//                    caller-owned `Diag` names the offending token.
+
+#import "modules/std.sx";
+#import "modules/std/cli.sx";
+
+report :: (label: string, ok: bool) {
+    if ok { print("{}: ok\n", label); } else { print("{}: FAIL\n", label); }
+}
+
+// Half-open containment [lo, hi) — used to prove a view points into argv.
+in_range :: (x: s64, lo: s64, hi: s64) -> bool {
+    return x >= lo and x < hi;
+}
+
+// True when `parse(args, cmds)` raised exactly `want`. Destructure binds
+// the error tag without `try`, so a bad vector never aborts the example;
+// the failing token is captured in the caller-owned `Diag`.
+raises :: (args: []string, cmds: []Command, want: CliError) -> bool {
+    d : Diag = .{};
+    _, e := parse(args, cmds, @d);
+    return e == want;
+}
+
+main :: () -> ! {
+    // ── Command table (caller storage; flag specs passed as views) ────
+    publish_flags : []FlagSpec = .[
+        FlagSpec.{ name = "out",     takes_value = true,  required = true  },
+        FlagSpec.{ name = "verbose", takes_value = false, required = false },
+    ];
+    status_flags : []FlagSpec = .[
+        FlagSpec.{ name = "verbose", takes_value = false, required = false },
+    ];
+    cmds : []Command = .[
+        Command.{ group = "ci", command = "publish", flags = publish_flags },
+        Command.{ group = "ci", command = "status",  flags = status_flags  },
+    ];
+
+    // ── 1. Valid: <group> <command> --flag v --bool --json ───────────
+    d : Diag = .{};
+    argv : []string = .["ci", "publish", "--out", "dist", "--verbose", "--json"];
+    p := try parse(argv, cmds, @d);
+
+    report("dispatch-group",   p.group == "ci");
+    report("dispatch-command", p.command == "publish");
+    report("dispatch-index",   p.cmd_index == 0);
+    report("flag-value",       p.value_of("out") == "dist");
+    report("flag-value-set",   p.is_set("out"));
+    report("bool-set",         p.is_set("verbose"));
+    report("json-set",         p.json);
+    report("no-rest",          p.rest.len == 0);
+
+    // ── 2. Heap discipline: flag value is a VIEW into argv ────────────
+    // "dist" is argv[3]; its bytes must lie inside that very element.
+    src   : s64 = xx argv[3].ptr;
+    stop  := src + argv[3].len;
+    pview : s64 = xx p.value_of("out").ptr;
+    report("value-is-view", in_range(pview, src, stop) or pview == src);
+    // group/command are argv[0]/argv[1] verbatim (same pointer, no copy).
+    g0 : s64 = xx argv[0].ptr;
+    gp : s64 = xx p.group.ptr;
+    report("group-is-view", gp == g0);
+
+    // ── 3. Dispatch to a different command in the table ──────────────
+    s_argv : []string = .["ci", "status", "--verbose"];
+    sp := try parse(s_argv, cmds, @d);
+    report("dispatch-2nd",   sp.command == "status" and sp.cmd_index == 1);
+    report("2nd-bool",       sp.is_set("verbose"));
+    report("2nd-json-unset", !sp.json);
+
+    // ── 4. `--` separator: rest are operand views, flags stop there ──
+    sep_argv : []string = .["ci", "publish", "--out", "dist", "--", "--raw", "x"];
+    spv := try parse(sep_argv, cmds, @d);
+    report("sep-value",   spv.value_of("out") == "dist");
+    report("sep-rest-len", spv.rest.len == 2);
+    report("sep-rest-0",  spv.rest.len == 2 and spv.rest[0] == "--raw");
+    report("sep-rest-1",  spv.rest.len == 2 and spv.rest[1] == "x");
+    report("sep-no-bool", !spv.is_set("verbose"));
+
+    // ── 5. First bare operand also stops flag parsing ────────────────
+    bare_argv : []string = .["ci", "publish", "--out", "dist", "extra", "tail"];
+    bpv := try parse(bare_argv, cmds, @d);
+    report("bare-rest-len", bpv.rest.len == 2);
+    report("bare-rest-0",  bpv.rest.len == 2 and bpv.rest[0] == "extra");
+
+    // ── 6. Value-flag accepts a single-dash value (not a long flag) ──
+    dash_argv : []string = .["ci", "publish", "--out", "-5", "--verbose"];
+    dpv := try parse(dash_argv, cmds, @d);
+    report("dash-value", dpv.value_of("out") == "-5" and dpv.is_set("verbose"));
+
+    // ── 7. Failures: each surfaces the specific variant ──────────────
+    a_unknown_cmd   : []string = .["ci", "deploy", "--out", "x"];
+    a_unknown_group : []string = .["zz", "publish", "--out", "x"];
+    a_too_few       : []string = .["ci"];
+    a_unknown_flag  : []string = .["ci", "publish", "--out", "x", "--nope"];
+    a_missing_value : []string = .["ci", "publish", "--out"];
+    a_value_eats    : []string = .["ci", "publish", "--out", "--verbose"];
+    a_missing_req   : []string = .["ci", "publish", "--verbose"];
+    report("err-unknown-cmd",     raises(a_unknown_cmd,   cmds, error.UnknownCommand));
+    report("err-unknown-group",   raises(a_unknown_group, cmds, error.UnknownCommand));
+    report("err-too-few",         raises(a_too_few,       cmds, error.UnknownCommand));
+    report("err-unknown-flag",    raises(a_unknown_flag,  cmds, error.UnknownFlag));
+    report("err-missing-value",   raises(a_missing_value, cmds, error.MissingValue));
+    report("err-value-eats-flag", raises(a_value_eats,    cmds, error.MissingValue));
+    report("err-missing-req",     raises(a_missing_req,   cmds, error.MissingRequired));
+
+    // ── 8. Diag names the offending token on the error path ──────────
+    de : Diag = .{};
+    _, ue := parse(a_unknown_flag, cmds, @de);
+    report("diag-flag-tag",   ue == error.UnknownFlag);
+    report("diag-flag-token", de.token == "--nope" and de.index == 4);
+
+    dm : Diag = .{};
+    _, me := parse(a_missing_req, cmds, @dm);
+    report("diag-req-tag",    me == error.MissingRequired);
+    report("diag-req-token",  dm.token == "out");
+
+    print("=== DONE ===\n");
+    return;
+}

examples/expected/0717-modules-cli-parse.exit

@@ -0,0 +1 @@
+0

examples/expected/0717-modules-cli-parse.stdout

@@ -0,0 +1,33 @@
+dispatch-group: ok
+dispatch-command: ok
+dispatch-index: ok
+flag-value: ok
+flag-value-set: ok
+bool-set: ok
+json-set: ok
+no-rest: ok
+value-is-view: ok
+group-is-view: ok
+dispatch-2nd: ok
+2nd-bool: ok
+2nd-json-unset: ok
+sep-value: ok
+sep-rest-len: ok
+sep-rest-0: ok
+sep-rest-1: ok
+sep-no-bool: ok
+bare-rest-len: ok
+bare-rest-0: ok
+dash-value: ok
+err-unknown-cmd: ok
+err-unknown-group: ok
+err-too-few: ok
+err-unknown-flag: ok
+err-missing-value: ok
+err-value-eats-flag: ok
+err-missing-req: ok
+diag-flag-tag: ok
+diag-flag-token: ok
+diag-req-tag: ok
+diag-req-token: ok
+=== DONE ===