fix(installer): mirror launch channel as default for external modules (#2321)

* fix(installer): mirror launch channel as default for external modules

When the user runs `npx bmad-method@next install`, the installer itself
runs from a prerelease, but the interactive channel gate previously hardcoded
"(all stable)" — defaulting tea/community modules to stable while bmad-method
itself was on next. The bleeding-edge launch did not flow through.

Detect the installer's own version via semver.prerelease() and default the
gate (and per-module picker) to match — "all next" for prerelease launches,
"all stable" for stable. Users keep full control: hit "n" to customize per
module, or pass explicit --channel / --pin / --next flags to override.

* fix(installer): seed channelOptions before module picker, not gate

CodeRabbit caught a label/install mismatch in the previous approach: the
module picker resolves version labels via decideChannelForModule, which runs
before _interactiveChannelGate. With channelOptions.global still null at
picker time, labels rendered from stable tags — then the gate flipped global
to 'next' and externals installed from main HEAD. Net effect on @next launches:
"tea (v1.6.0)" in the picker, but install pulled HEAD.

Move the launch detection up into promptInstall, immediately after
parseChannelOptions. Seeding channelOptions.global = 'next' before the picker
makes labels resolve from main HEAD (matching the install) and lets the
existing gate's haveFlagIntent check skip cleanly — the @next user already
declared their intent by typing it. Per-module customization remains available
via --pin / --next / --channel flags, same as for any pre-set global.

tools/installer/ui.js

@@ -2,6 +2,7 @@ const path = require('node:path');
 const os = require('node:os');
 const semver = require('semver');
 const fs = require('./fs-native');
+const installerPackageJson = require('../../package.json');
 const { CLIUtils } = require('./cli-utils');
 const { ExternalModuleManager } = require('./modules/external-manager');
 const { resolveModuleVersion } = require('./modules/version-resolver');
@@ -128,6 +129,24 @@ class UI {
       await prompts.log.warn(warning);
     }
 
+    // When the user launched the installer from a prerelease (npx bmad-method@next),
+    // mirror that intent for external modules: seed the global channel to 'next' so
+    // the module picker's version labels resolve from main HEAD (matching what
+    // actually gets installed) and the interactive channel gate skips — the user
+    // already declared "next" intent by typing @next. Explicit channel flags
+    // override this seed.
+    if (
+      semver.prerelease(installerPackageJson.version) !== null &&
+      !channelOptions.global &&
+      channelOptions.nextSet.size === 0 &&
+      channelOptions.pins.size === 0
+    ) {
+      channelOptions.global = 'next';
+      await prompts.log.info(
+        'Launched from a prerelease — installing all external modules from main HEAD (next channel). Pass --all-stable or --pin to override.',
+      );
+    }
+
     // Get directory from options or prompt
     let confirmedDirectory;
     if (options.directory) {
@@ -332,8 +351,10 @@ class UI {
 
     // Interactive channel gate: "Ready to install (all stable)? [Y/n]"
     // Only shown for fresh installs with no channel flags and an external module
-    // selected. Non-interactive installs skip this and fall through to the
+    // selected. Skipped for prerelease launches because channelOptions.global
-    // registry default (stable) or whatever flags were supplied.
+    // was already seeded to 'next' upstream. Non-interactive installs skip this
+    // and fall through to the registry default (stable) or whatever flags were
+    // supplied.
     await this._interactiveChannelGate({ options, channelOptions, selectedModules });
 
     let toolSelection = await this.promptToolSelection(confirmedDirectory, options);
@@ -1783,7 +1804,9 @@ class UI {
    *
    * Skipped when:
    *   - running non-interactively (--yes)
-   *   - the user already passed channel flags (--channel / --pin / --next)
+   *   - the user already passed channel flags (--channel / --pin / --next), OR
+   *     the installer was launched from a prerelease (which seeds
+   *     channelOptions.global = 'next' upstream in promptInstall)
    *   - no externals/community modules are selected
    *
    * Mutates channelOptions.pins and channelOptions.nextSet to reflect picker choices.