[metif12]

What this adds

Two things from the same part of the roadmap: the three gates that were
unreachable, and the onboarding that did not exist.

Check, vet, and format

• V: Check runs v -check, which type-checks without producing a binary
• V: Vet runs v vet -W, which reports suspicious constructs and treats
  warnings as errors — the one to use in CI
• V: Format Check runs v fmt -verify, which reports whether the formatter
  would change anything

None of these was reachable from the extension. The v-workflow skill documents
v -check and v fmt -verify as the two that gate everything else, so a user
following the skill's advice had to leave the editor to follow it.

Each works on the active file when one is open, and on the workspace otherwise,
matching how Run and Test already behave. All three surface through the vls
problem matcher, so a failure lands in the Problems panel at the right line rather
than only in the task output.

The flags were verified against the compiler before writing the args:

command	clean file	file with a problem
v -check file.v	exit 0	exit 1
v vet -W file.v	exit 0	exit 1 on warnings
v fmt -verify file.v	exit 0	exit 1 when not formatted

Welcome walkthrough

There was no onboarding. Tasks, CodeLens, coverage and the agent commands were
only discoverable from the README, so a user who did not read it had no way to
learn that V: Check or the coverage status item existed.

The walkthrough has three steps, each completing when the command it describes has
been run: install V, build/run/test, and check/vet/format. That walks a new user
through the extension's own commands rather than asking them to read
documentation first.

The agents step is deliberately absent. It would describe v mcp and v skills, which are not on this branch, and a walkthrough step for a command that
does not exist is worse than no step. It can be added when #558 and #559 merge.

Verification

npm run lint, npm run lint:md, npm run test:grammar, npm run build and
npm run package all pass.

npm test reports 24 tests, 21 pass, 3 fail. The three failures are the
pre-existing Windows path-separator tests on master, fixed in
#561 and not touched here.
This branch is based on master rather than #556, so it carries none of those
fixes; the three failures are the same three, unchanged.

Proof the new tests catch something, each reverted:

1. replaced the v.mod probe in standaloneTaskScope with if (false) →
   uses the nearest V project root for standalone saves and coverage red
2. removed the v.vls.openOutput entry from contributes.commands →
   declares every registered command red, naming the id
3. removed markdownDeprecationMessage from vls.args →
   declares every legacy setting red, naming the key
4. pointed a walkthrough step at a missing file →
   ships a walkthrough whose steps point at files that exist red, naming the step

My first attempt at (3) used a regex that silently matched nothing and the test
stayed green. I redid it through the parsed object, which is the version reported
above — a sabotage that does not apply proves nothing about the test.

Relation to other PRs

Independent of #556, #557, #558, #559 and #560. It touches taskSpec.ts,
vTasks.ts, package.json, README.md, CHANGELOG.md and walkthrough/, none
of which the other PRs modify in a conflicting way.

[metif12]

Closing as superseded by #583, which is this branch's tree plus three files.

Both are based on 55cec96. git diff origin/feat/check-vet-fmt-tasks origin/feat/walkthrough-debug is exactly three files: package.json (+10/-1,
the walkthrough description text and the new debugging step), src/taskSpec.ts
(+3/-1, a prettier reformat of taskActionTitle) and walkthrough/debugging.md
(+18, new). This branch's own file set is a strict subset of #583's, and no content
here is absent from #583.