refactor(parse): require exact command and flag names

PLAN.md

@@ -452,14 +452,10 @@ Groups are the opposite case: `Command::get_groups`, `ArgGroup::get_args` and
       carries doc-comment or explicit help, hidden canonical values, hidden `alias`,
       visible `visible_alias`, and case-insensitive matching through its static metadata
       and lossless KDL emission.
-- [x] **`infer_subcommands` / `infer_long_args`** — unambiguous prefixes of
-      command names, command aliases, long flags, and long aliases are accepted
-      only when one declaration matches. Both settings are inherited by child
-      commands and carried through KDL, usage-lib, generated Rust, generated Go,
-      and Go's runtime spec builder. `#[usage(infer_subcommands, infer_long_args)]`
-      is the typed spelling. clap exposes setters but no public getters for these
-      global settings, so `clap_usage` cannot recover them from an existing
-      `Command`; a migration declares them on the usage type.
+- [x] **`infer_subcommands` / `infer_long_args` are intentional non-goals.** Long
+      flags and subcommands require exact spellings. Diagnostics may suggest what
+      was probably meant, but accepting a prefix would let a later declaration
+      change or invalidate an existing invocation.
 - [x] **`external_subcommand`** — an unmatched word is forwarded with the rest
       of argv. Spec `external_subcommand`, usage-lib, usage-argv, the derive
       (`#[usage(external_subcommand)]` on a catch-all `Vec` variant), and the

argv/src/help.rs

@@ -1249,7 +1249,6 @@ pub fn route_to<'t>(
     if route.is_empty() {
         route.push(root);
     }
-    let mut infer_subcommands = route.iter().any(|cmd| cmd.infer_subcommands);
 
     // Already there for `--help`, whose span is empty. For the `help` word the parse stopped at
     // the command that *saw* it, and the words naming the one being asked about are exactly the
@@ -1270,13 +1269,8 @@ pub fn route_to<'t>(
         // that reached here did. Matching on name and alias together instead answered with
         // whichever subcommand came first, which for a colliding word is a different command
         // than the one the parser selected.
-        let next = if infer_subcommands {
-            crate::find_prefixed(here, word)?
-        } else {
-            crate::find_named(here, word)?
-        };
+        let next = crate::find_named(here, word)?;
         route.push(next);
-        infer_subcommands |= next.infer_subcommands;
     }
     // Only if the walk actually arrived: a caller should fall back rather than be handed a
     // page about some other command.