feat(UI): import preview page with entity diff and normalisation decisions

[pskillen]

Problem

Import today stops at aggregate counts in a confirm modal (previewImportMerge → ImportMergeReport with added/updated/unchanged/removed per entity type). Operators cannot see which channels, zones, contacts, talk groups, or RX group lists will land in the project, what field-level changes merge would apply, or what normalisation decisions the adapter made before merge.

Flow	Today	Gap
New project (Home → ImportDropzone)	Parses files and creates project immediately	No preview step; no continue/cancel
Active project (ImportIntoActivePanel on Import & export)	Modal with file summary + count lines	No per-entity list; no field diff; no visibility into merge heuristics

#58 shipped merge/overwrite with a lightweight confirm modal and explicitly deferred field-level diffs to a follow-up. This ticket is that follow-up, expanded to both import entry points and future import normalisation features.

Intended outcome

A dedicated import preview step in the import workflow — a route or full-page panel (not only a modal) — that runs before any codeplug is created or mutated. The operator reviews what will happen, then continues or cancels.

Preview content (all adapters)

For the selected vendor format / adapter, show a structured preview of the parsed import result before apply:

Section	Contents
Files	Recognised, skipped, and error files (existing ImportResult messages)
Channels	List of channels to import — name, mode, frequencies, key refs
Zones	Zone names + member channel names (resolved where possible)
Contacts / talk groups / RX group lists	Names and membership summaries
Warnings	Unresolved zone members, parse warnings, profile-specific notes

Adapter-agnostic UI: entity shapes come from internal ImportResult / parsed models, not vendor column names in the preview layer.

Normalisation decisions (show when applicable)

When import adapters apply best-effort collapse heuristics, the preview must surface what was decided — not silently merge:

Feature	Issue	Preview should show
Multi-mode channel merge	#46	e.g. "Merged GB7GL + GB7GL DMR → one multi-mode channel (FM + DMR)" or "Left as 2 separate channels (ambiguous)"
Multi-talkgroup channel collapse	#36	e.g. "Collapsed GB7XX TG235 + GB7XX TG2351 → one logical channel with 2 talk groups"
Other adapter warnings	—	Any ImportMessage with severity warning tied to a decision

Decisions belong in ImportResult (or a sibling ImportPreview type) at the import boundary — the UI only renders them.

Merge / overwrite diff (active project only)

When importing into an existing codeplug with merge or overwrite mode, show the diff that would be applied against the active project:

Change type	Per entity	Detail level (v1 target)
Added	Channels, zones, contacts, TGs, RGLs	Name + summary fields (mode, freqs)
Updated	Same	Name + changed fields (field-level diff where importEntityCompare detects inequality)
Removed	Same (overwrite mode)	Names of rows that will be dropped
Unchanged	Collapsed by default	Expandable count

Reuse / extend previewImportMerge and importEntityCompare.ts to return entity-level change lists, not only EntityImportStats aggregates.

For overwrite, clearly warn which entire entity arrays will be replaced (existing behaviour) and list removed names.

Workflow integration

flowchart TD
  Drop["Drop files / folder"] --> Parse["importFiles → ImportResult"]
  Parse --> Preview["Import preview page"]
  Preview --> Cancel["Cancel — no mutation"]
  Preview --> Continue["Continue"]
  Continue --> NewProj["importNewProject (Home)"]
  Continue --> ActiveMerge["applyImportToActive (Import & export)"]

Loading

1. New codeplug from import (Home) — after parse, navigate to preview with parsed payload in session/state; Continue creates the project; Cancel returns without side effects.
2. Merge / overwrite (Import & export) — after parse + mode selection, navigate to preview showing diff vs active codeplug; Continue calls applyImportToActive; Cancel discards pending import.

Replace or supersede the current ImportIntoActivePanel confirm modal with the preview page (modal may remain for trivial no-change cases if desired).

UX notes

• Preview is read-only — no inline editing of import rows in v1.
• Group by entity type; filter/search for large codeplugs.
• Show merge mode (merge vs overwrite) prominently on active-project preview.
• "No changes" path: short message + Close (idempotent re-import).

Affected

• New route e.g. /import/preview (or nested under home / import-export) + page component
• src/lib/importMerge.ts — extend preview to return entity-level diffs
• src/lib/importEntityCompare.ts — optional field-level diff helper
• src/lib/import/types.ts — ImportDecision / normalisation notes from adapters
• src/components/ImportDropzone/ — defer apply; hand off to preview
• src/components/ImportIntoActivePanel/ — wire preview page instead of modal-only flow
• src/state/codeplugStore.tsx — pending import state (session or transient store slice)
• Tests: unit (diff builder), component (preview page), system (importWorkflow.ts)
• Docs: docs/features/import-export/README.md, component sidecar

Notes / dependencies

• Builds on #58 (active import + previewImportMerge) and #7 (adapter registry).
• Pairs with #46 and #36 — preview must expose their merge/collapse decisions when those features ship; design the ImportDecision shape now so adapters can populate it incrementally.
• Vendor boundaries: diff compares internal model fields; wire column names stay in adapter/reference docs only.
• Privacy: parsed import stays in browser memory / session until Continue; never commit operator exports.

Out of scope

• Editing import rows on the preview page (change in CRUD after import instead).
• Three-way merge or conflict resolution UI (imported values win on update).
• Undo after Continue (operator re-imports a backup).
• Export preview (separate concern).

Workflow note

Branch from origin/main, atomic conventional commits (preview data layer → page UI → wire Home + active flows → tests/docs), PR linking Closes #N. Pair with docs/features / progress-tracking skills for multi-slice work.