fix: keep process type resolvable with heroku run --exit-code

[michaelmalave]

Summary

Fix heroku run --exit-code <process-type> failing with command not found (exit 127). When --exit-code was set, the CLI appended ; echo … directly onto the command (web → web;), so the runtime's first-token lookup no longer matched a declared process type and ran the name literally in a shell. Adding a space before the ; keeps the first whitespace-delimited token bare so the runtime resolves it against the app's Procfile/formation.

• Fix command wrapping in Dyno._doStart to emit <command> ; echo … instead of <command>; echo ….
• Add _doStart unit tests covering single-token process types, multi-arg commands, and the no---exit-code path.

Type of Change

• fix: Bug fix or issue (patch semvar update)
• feat: Introduces a new feature to the codebase (minor semvar update)
• perf: Performance improvement
• docs: Documentation only changes
• tests: Adding missing tests or correcting existing tests
• chore: Code cleanup tasks, dependency updates, or other changes

Note: Add a ! after your change type to denote a breaking change.

Verification

Automated:

npx mocha --forbid-only "test/unit/lib/run/dyno.unit.test.ts"
npx eslint src/lib/run/dyno.ts test/unit/lib/run/dyno.unit.test.ts

Manual (against a real app with a web process type):

npm run build   # oclif runs from ./dist, so rebuild before exercising the CLI
./bin/run run --exit-code web -a example-http-proxy

• Before: bash: web: command not found, exit code 127.
• After: the app's Procfile command runs (node mcp-auth-proxy/index.js), and the CLI passes through the app's real exit code instead of 127.

Additional Context

Root cause is server-side resolution: the runtime looks up a process type by the first whitespace-delimited token of the command (app.process_types.find_by(name: normalized_command.split(/\s+/).first)), then substitutes the real command while keeping trailing args. web; matched nothing, so web ran verbatim. The one-character fix (space before ;) keeps the token web and leaves ; echo … as trailing shell, preserving exit-code propagation. The change flows through run, run:inside, and rake, which all route through Dyno.

Reproduction:

• heroku run web → works.
• heroku run --exit-code web → expected: process type runs and its exit code is returned; actual (before fix): command not found, exit 127.

Related Issue

Closes #1227

[sbosio]

LGTM!