enhance(#2971): strict planning filter mode for /gsd-pr-branch (#3720)

* test(#2971): failing-first suite for the pr-branch planning-path filter

Binds the not-yet-built planning.pr_strict mode and the corrected filter recipe
for /gsd-pr-branch across six layers: pure classification and forbidden-path
predicates, real-git fixtures that run the cherry-pick filter loop end to end,
config-key registration through the real CLI and both manifests, the executed
worktree-materialization claim the issue's triage asked to establish, fast-check
properties over arbitrary path sets, and a drift guard over the shipped workflow.

Two live defects in today's shipped recipe are pinned as regressions, both
reproduced empirically first: `git rm -r --cached` stages a deletion of any
.planning/ path the target branch already tracks, so the generated PR removes the
base branch's planning files; and the same command leaves the cherry-picked file
untracked on disk, so a second commit touching that path aborts the pick with
"untracked working tree files would be overwritten" and every remaining commit is
silently dropped.

The test helper parses the canonical path lists out of gsd-core/workflows/pr-branch.md
rather than restating them, so the workflow stays the single source of truth and the
suite cannot drift from what ships.

Refs #2971

* feat(#2971): strict planning filter mode for /gsd-pr-branch

Adds planning.pr_strict — a boolean, default false, that selects what
/gsd-pr-branch means by "filtered". Default mode is unchanged: structural
planning state survives into the PR branch and the nine transient
subdirectories do not. Strict mode drops every .planning/ path, structural
files included, and carries a commit over only when it touches at least one
file outside .planning/.

Strict mode is what makes planning.commit_docs: true safe for a project that
versions its planning tree locally but publishes none of it. The alternative
posture, commit_docs: false, silently costs parallel executor isolation — a
worktree is checked out from a commit, so an untracked or ignored .planning/
is simply absent inside it and the executor has no PLAN.md to read. That claim
is now established by an executed fixture rather than inherited.

The two path lists are declared once and both projections derived from them,
so create_pr_branch and verify can no longer disagree about what the filter
promised. verify previously counted every .planning/ path against a documented
success criterion of zero while create_pr_branch was specified to preserve five
structural files, so a correct run reported itself as failed on every phase
that touched STATE.md — which is every phase. It now asserts against the active
mode, and names the .planning/ paths default mode deliberately keeps rather
than trading a wrong signal for silence.

Two verified defects in the same recipe are fixed alongside, because strict
mode would have amplified both. `git rm -r --cached` staged a deletion for any
.planning/ path the target branch already tracked, so the generated PR removed
the base branch's planning files — under strict mode that would have been the
entire tree. The same command left the picked file untracked on disk, so a
second commit touching that path aborted the cherry-pick with "untracked
working tree files would be overwritten" and every remaining commit was
silently dropped. Both were reproduced against real git before being fixed.
The filter now forces excluded paths back to what the PR branch's HEAD carries,
in the index and the working tree; a conflict outside the filter halts instead
of being improvised past; a commit left empty by filtering is skipped rather
than failing. A clean-working-tree precondition makes the worktree half safe.

Closes #2971

* fix(#2971): unwind the checkout on a conflict halt, and test the real recipe

Two review findings, both fixed in place.

The isolated adversarial pass found that the conflict-outside-the-filter branch
exited while leaving the user checked out on the half-built PR branch with
cherry-pick state still live — this loop runs in the user's own working
directory, so stranding them there is a real cost even though it is not a
vulnerability. The branch now aborts the pick, returns to the original branch,
removes the partial PR branch, and says so before exiting.

The standards pass found the L2 fixtures executed a hand-written mirror of the
cherry-pick filter recipe rather than the recipe itself, so a reordering in the
workflow would not have been caught — and the order is load-bearing, since
restoring a path from HEAD before removing it inverts the filter. The helper now
extracts the canonical loop from the shipped workflow and the fixtures execute
that verbatim, which also gives the conflict-halt unwind above real coverage.
The drift guard additionally pins the two commands' relative order and asserts
the workflow carries exactly one canonical loop.

Also records the publication gate in the CONTEXT.md glossary next to the commit
gate it is distinct from.

Refs #2971

* fix(#2971): make the conflict-halt unwind actually unwind, and use the colon slash form

The remote matrix caught two defects in the previous commit.

The halt path claimed to restore the original branch but did not. `git
cherry-pick --abort` does not apply to a single `--no-commit` pick with no
sequencer file, and the fallback left the unmerged index in place, which makes
`git checkout` refuse — a failure the `2>/dev/null || true` then swallowed, so
the user was told they had been restored while still sitting on the half-built
PR branch. The unwind now drops sequencer state, hard-resets the disposable PR
branch to clear the unmerged index, and only claims a restore when the checkout
actually succeeded; when it does not, it says where the user is and gives them
the two commands to finish it by hand. Verified against real git: exit 1, the
conflict named, HEAD back on the original branch, the partial branch gone, a
clean tree and no CHERRY_PICK_HEAD.

Two runtime-loaded source artifacts used the retired `/gsd-<cmd>` hyphen form,
which names a command no runtime registers. The canonical authoring token for
workflows and references is `/gsd:<cmd>`; docs keep the hyphen form, so the
documentation added in this branch is unaffected. The comment in src/config.cts
moves to the colon form too, since it propagates into the generated lib.

Refs #2971

* docs(#2971): backfill PR number into the changeset fragments (#3720)

---------

Co-authored-by: sim <sim@local>

docs/how-to/publish-prs-without-planning-artifacts.md

@@ -0,0 +1,113 @@
+# Publish PRs without planning artifacts
+
+You want GSD's `.planning/` tree versioned in git on your own branch — so parallel executors can
+read their plans and `/gsd-undo` has something to restore — while the pull request your team
+reviews contains none of it.
+
+This is the opposite trade to
+[Keep planning docs out of a shared repo](keep-planning-docs-private.md), which removes planning
+from git entirely and loses worktree isolation in the process. Use this guide when you want the
+history and want the remote clean.
+
+Five steps, and the fourth is the one that decides whether the guarantee actually holds.
+
+## 1. Keep planning artifacts committed
+
+```bash
+gsd-tools config-set planning.commit_docs true
+```
+
+This is already the default. Set it explicitly if someone previously turned it off, or if
+`.planning/` is listed in `.gitignore` — a gitignored `.planning/` auto-resolves `commit_docs` to
+`false` no matter what `config.json` says, and `planning.pr_strict` cannot filter what was never
+committed.
+
+If `.planning/` is currently in `.gitignore`, remove that line before continuing.
+
+## 2. Turn on strict PR filtering
+
+```bash
+gsd-tools config-set planning.pr_strict true
+```
+
+Confirm it took:
+
+```bash
+gsd-tools query config-get planning.pr_strict --raw
+```
+
+`true` means every `.planning/` path will be filtered out of the generated PR branch —
+`STATE.md` and `ROADMAP.md` included, not only the per-phase artifacts.
+
+## 3. Do the work normally
+
+Nothing about the phase loop changes. `/gsd-plan-phase` and `/gsd-execute-phase` commit planning
+artifacts exactly as they always have, executor worktrees find their `PLAN.md`, and your working
+branch carries the full planning history.
+
+## 4. Generate the PR branch — and push *that* branch
+
+```bash
+/gsd-pr-branch
+```
+
+The command creates `<your-branch>-pr` from the target branch and rebuilds the history without any
+`.planning/` path. **Push the generated `-pr` branch, never your working branch** — the working
+branch is where the planning history lives, and it is the one thing that must not reach the remote.
+
+```bash
+git push origin <your-branch>-pr
+gh pr create --base main --head <your-branch>-pr
+```
+
+Requirements before it will run:
+
+- **A clean working tree.** Uncommitted changes are rejected up front. Commit or stash first.
+- **Commits ahead of the target.** With none, the command exits without creating a branch.
+
+## 5. Read the verification summary
+
+The run ends with a summary. Two lines carry the guarantee:
+
+```
+Mode: strict
+Planning paths in diff: 0 (allowed 0, forbidden 0 — must be 0)
+```
+
+`forbidden` is the number that matters. In strict mode it counts every `.planning/` path that
+survived into the branch, and it must be `0`. `allowed` is always `0` in strict mode — there is no
+allowed population.
+
+### What each outcome means
+
+| Summary line | Meaning | What to do |
+|---|---|---|
+| `Mode: strict` … `forbidden 0` | The guarantee held. | Push the `-pr` branch. |
+| `Mode: default` | `planning.pr_strict` did not resolve to `true`. | Re-run step 2; the key is read from the project's `.planning/config.json`, so check you are in the right project root. |
+| `forbidden` greater than `0` | The filter did not remove everything it promised. | Do **not** push. This is a bug — report it with the listed paths. |
+| `Conflict outside the .planning/ filter` | A real content conflict between your commits and the target branch. | Resolve it on your working branch, then re-run `/gsd-pr-branch`. |
+| `Working tree has uncommitted changes` | Step 4's precondition failed. | Commit or stash, then re-run. |
+| `No commits ahead of <target>` | There is nothing to filter. | Not an error — you have not committed anything yet, or the target is wrong. |
+
+An `ℹ️` advisory listing `.planning/` paths appears only in **default** mode, naming paths that are
+neither transient nor structural (`config.json`, `intel/`, `workstreams/`) and therefore kept. Strict
+mode removes those too, so the advisory never appears — if you see it, you are not in strict mode.
+
+## Verify it for yourself
+
+Before trusting the setup on a real review, confirm the generated branch is clean:
+
+```bash
+git diff --name-only main..<your-branch>-pr | grep '^\.planning/'
+```
+
+No output is the expected result. Any output means step 2 did not take effect, or the run reported
+a non-zero `forbidden` count you should not push past.
+
+## Related
+
+- [Keep planning docs out of a shared repo](keep-planning-docs-private.md) — the other posture:
+  planning never enters git, at the cost of parallel executor worktrees
+- [Planning settings reference](../CONFIGURATION.md#planning-settings) — `planning.pr_strict`,
+  `planning.commit_docs`, and the rest of the `planning.*` keys
+- [`/gsd-pr-branch` reference](../COMMANDS.md#gsd-pr-branch)