fix: keep a saved prompt variable open and guard unsaved edits (#6023)

[atomantic]

Summary

The Prompt Manager's Variables tab treated a successful save like a reset. saveVariable cleared ?var= from the URL and blanked every field with { silent: true } suppressing the only feedback, so editing Tone Guide and clicking Save dropped the user into an empty "New Variable" form with no toast — indistinguishable from a crash. Verifying what had just been written meant finding the variable in the list and clicking it again. Creating a variable landed the same blank form instead of opening what was created, and deleting one finished in silence.

Separately, the list was destructive: variable content runs to paragraphs of prompt instructions, and clicking another row (or the "+") overwrote varForm immediately, with no way back.

What changed (client/src/pages/PromptManager.jsx)

Save / create / delete feedback

• Saving an existing variable keeps it selected and keeps the saved text in the form, and toasts Variable "<name>" saved. The post-save loadData() cannot re-hydrate over it — varHydratedRef still holds the open key.
• Creating toasts Variable "<key>" created and adopts the new key as ?var=<key> — after the refreshed list holds it, so the "variable could not be found" panel can't flash on the way in.
• Deleting toasts Variable "<name>" deleted.
• A save that lands after the user has moved on re-baselines nothing, so it can't stamp the outgoing variable's text as the incoming one's saved state.

Unsaved-edit guard

• savedVarForm tracks the last server-confirmed form as a full copy (not a boolean), so typing an edit and undoing it stops counting as dirty.
• The open list row and the editor header show an Unsaved badge / Unsaved changes note while dirty.
• Clicking another variable, or the "+", parks the request in pendingVar and turns that slot into a Discard / Keep editing InlineConfirmRow instead of switching. The "+" has no row of its own, so its question takes the top of the list.
• Create-mode drafts count as dirty too — a typed-but-unsaved new variable is exactly the work "+" would otherwise throw away.
• Arming a delete disarms a pending switch and vice versa, so a row is never asking two questions at once.

This is the same inline-confirmation shape the Stages (#6021) and Job Skills (#3939) tabs already use. No window.confirm; selection stays in the URL.

Test plan

client/src/pages/PromptManager.test.jsx — new PromptManager variable editing suite (8 tests). All 8 verified failing against the pre-fix component (swapped in origin/main's PromptManager.jsx, ran the suite, restored):

• saved variable stays open, keeps its edited content, and toasts — asserted against a refetch that still returns the pre-save fixture, which is the re-hydration regression
• created variable toasts and lands in ?var=<key> with its content intact
• delete toasts
• editing then clicking another variable arms the discard row rather than switching
• "Keep editing" preserves the edits and the selection
• "Discard" switches to the clicked variable
• "+" asks first, then opens the blank form
• undoing an edit back to the saved value disarms the question — no prompt on the next click

cd client && npx vitest run src/pages/PromptManager.test.jsx
  Tests  71 passed (71)

Full client suite: 832 passed | 1 skipped. The one intermittent failure seen on one run was src/components/ui/PageSkeleton.test.jsx (getAllByRole('status')[0] / aria-busy), which passes in isolation across repeated runs and is untouched by this diff.

npx biome check clean on both changed files.

Closes #6023

https://claude.ai/code/session_01RA3pD5YM2dukQwbZ3pC6WA