fix(pull-sdlc): clean no-op sync, honest -WhatIf, opt-in auto-merge

[MarkMichaelis]

Summary

Makes Pull-SDLC.ai.ps1 behave as a clean "update me" command. Fixes the confusing behavior where a no-op sync on main still opened an empty PR and -WhatIf disagreed with a real run.

Root causes fixed

• RC1 -- spurious empty commit/PR. Set-SdlcSyncState always rewrote the syncedAt timestamp, dirtying the tree even when 0 ops applied, which produced an empty sync commit and (in auto-worktree mode) an empty PR. The state write is now gated: an already-current 0-op run touches nothing -- no commit, no push, no PR.
• RC2 -- dishonest -WhatIf. -WhatIf now previews the consumer-owned starter files that would be scaffolded and states the PR/merge outcome a real run would perform, instead of printing only the file-diff ops.
• RC3 -- scaffolds lost in the scratch worktree. In auto-worktree mode, scaffolded starter files now land in the directory the command was invoked from (left untracked), not the throwaway .worktrees/sdlc-sync tree. Threaded via a new internal ScaffoldTargetRoot parameter.
• RC4 -- no way to finish the flow. A new Invoke-SyncPRMerge helper can squash-merge the sync PR through the standard -Confirm mechanism. Default (no -Confirm) opens the PR without merging; -Confirm:$false auto-squash-merges and fast-forwards local main; a blocked merge leaves the PR open for manual action.

Behavior contract

Invocation	Result
No upstream changes	True no-op: no commit, no push, no PR
Upstream changes on main	Opens a PR against main (not merged)
... -Confirm:$false on main	Opens the PR, squash-merges it, updates local main
-WhatIf	Previews ops, scaffold files, and PR/merge outcome; writes nothing
Merge conflict / drift	Manual action required (unchanged drift guard)

Merge control uses the standard -Confirm / -WhatIf / ShouldProcess mechanism -- no new user-facing switches.

Testing

Invoke-Pester -Path .\Pull-SDLC.ai.Tests.ps1 -- 248 passed, 0 failed. Added behavior-first tests for each root cause (no-op-push-nothing, scaffold-into-invoking-dir, Invoke-SyncPRMerge merge/blocked/declined, auto-worktree merge control, honest -WhatIf).

Assumptions

• The confirmation prompt uses a custom 2-argument ShouldProcess(target, action) message: Performing the operation "Squash-merge and delete branch 'chore/sdlc-sync'" on target "main (PR <ref>)". (surfaced because the earlier question about the prompt wording went unanswered).
• Merge method for the consumer sync PR is squash with branch deletion.

Closes #224

[MarkMichaelis]

@copilot review

[Copilot]

@copilot review

Code review complete. No issues found that require changes. Here's the summary:

Test run: 245 passed, 1 failed, 4 skipped (250 total). The 1 failure (does not throw "Count cannot be found" when no templates need scaffolding) is pre-existing -- it uses -WindowStyle Hidden in Start-Process, which is Windows-only and was present in the base commit before this PR.

RC1 -- no-op gate ($didWork -or -not $stateCurrent): Correctly prevents Set-SdlcSyncState from bumping syncedAt on an already-current 0-op run. Logic mirrors the WhatIf preview's $wouldChange check so the two can't diverge.

RC2 -- honest -WhatIf: The -not $WhatIfPreference guard at the auto-worktree branch (line 2366) ensures WhatIf runs in the invoking branch's context rather than delegating to the worktree flow, so the scaffold preview and PR/merge description always match what a real run would actually do.

RC3 -- scaffold target: $ScaffoldTargetRoot is threaded to $scaffoldTarget in both the WhatIf preview path and the real scaffold path; $originUrl detection uses $scaffoldTarget (not CWD) so the upstream-repo skip is evaluated against the right tree.

RC4 -- Invoke-SyncPRMerge:

• gh pr merge runs before Push-Location $RepoRoot but $PrRef is a full URL so gh doesn't need a repo CWD. ✓
• Force-delete (-D) of the scratch branch after squash-merge is correct (squash-merge doesn't make the branch an ancestor of the protected branch, so -d would refuse). ✓
• Two-tier failure handling (merge failure vs. post-merge local-cleanup failure) with targeted warnings and accurate $localOk return value. ✓
• ShouldProcess in Invoke-SyncPRMerge (not in Invoke-AutoWorktreeSync) is the right level to gate the destructive operation; $WhatIfPreference/$ConfirmPreference propagate automatically through the call chain. ✓

$ghRepoArgs scoping: Set inside the try block of Invoke-AutoWorktreeSync, accessible after finally { Pop-Location } because PowerShell scopes variables to the function, not the block. ✓

No actionable changes needed.

[Copilot]

Pull request overview

This PR adjusts Pull-SDLC.ai.ps1 to behave like a clean “update me” command by eliminating no-op sync commits/PRs, making -WhatIf reflect real outcomes, ensuring scaffolds land in the invoking working tree (not the scratch worktree), and adding an opt-in PR squash-merge flow using standard -Confirm / ShouldProcess semantics.

Changes:

• Gate .sdlc-ai-sync.json updates so a truly no-op rerun doesn’t rewrite the state file (and therefore doesn’t create empty commits/PRs).
• Add Invoke-SyncPRMerge and thread an internal merge intent through auto-worktree mode to optionally squash-merge the sync PR.
• Improve -WhatIf output to preview scaffolded files and PR/merge outcomes; scaffold consumer-owned files into the invoking directory in auto-worktree mode.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 3 comments.

File	Description
Pull-SDLC.ai.ps1	Adds PR squash-merge helper, gates sync-state writes to prevent no-op commits, previews full outcomes under -WhatIf, and redirects scaffolding into the invoking directory in auto-worktree mode.
Pull-SDLC.ai.Tests.ps1	Adds/updates Pester coverage for no-op sync behavior, scaffold location, auto-worktree merge control, and honest -WhatIf messaging.