feat(lifeboard): export and restore

[ivanmkc]

The stack

#	PR	What it adds	Tests at this point
1	#311	A real localStorage for the test suite on Node 25	viewer 747
2	#312	@ivanmkc/termchart-canvas; injectable interact transport	canvas 473 · viewer 278
3	#313	lifeboard PWA: fact log, boards, service worker	lifeboard 36
4	#314	Shell, family profiles, tap layer	lifeboard 82
5	#315	The agent turn, four providers, Connections	lifeboard 142
6	#316	Packs, recipes, shopping-list arithmetic	lifeboard 231
7	#317	Provenance and lineage	lifeboard 257
8	#318	Calendar, Gmail, mail triage	lifeboard 301
9	#319	The bridge and long jobs	cli 314 · lifeboard 320
10	#310	Proactivity, scheduled boards, Google sign-in	cli 320 · lifeboard 343
11	#320	Persistence audit fixes: multi-tab, stale builds, no-storage boot	lifeboard 350
12	#321	User guide, bridge setup, QA guide, persistence audit	lifeboard 350
13	#322	A plan for third-party integrations (docs only)	unchanged
14	#323	A practice drill a board can define: audio + Q&A	canvas 485 · lifeboard 372
15	#325	Export and restore	lifeboard 389
16	#326	Draft a message, approve it, then send	lifeboard 399
17	#327	Hand long work to the Mac	lifeboard 406
18	#328	A Packs screen, and authoring one by describing it	lifeboard 418
19	#329	Activity — what changed, who changed it, undo	lifeboard 428
20	#330	Four defects found reviewing the stack	cli 323 · lifeboard 431

Every branch in the stack was checked out on its own and verified independently: npm install, tsc --noEmit for every package, npm test across the workspace, and the offline e2e where it exists. All twenty are green — no branch depends on a later one to build or pass. Full viewer e2e (11 suites, 106 assertions) was run on #312 as the behaviour-preservation evidence for the extraction.

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Stack position: 15 of 19. Base: lifeboard/13-practice.

Closes the finding the persistence audit called the largest remaining risk, and the cheapest to fix: everything lifeboard knew lived in one browser's IndexedDB, and "clear site data" took the calendar, the lists and the vaccination dates with it. The durable state is an array of entries, so export is serialising it and restore is putting it back.

Restore replaces; it does not merge. Two logs that grew independently both number their entries from 1, and deciding which "seq 7" wins is a guess dressed up as a policy. Merging devices is a real feature that needs a real design; pretending this is that would lose someone's records quietly. So the screen shows what is here, what is in the file, and that there is no undo — and waits.

Reading a backup is strict on purpose. This is the one path that overwrites everything: the format, the version, every entry's shape and collection, and duplicate sequence numbers are all checked, and the error names the offending entry.

Adds Backend.replace and Store.restore — the only thing in the codebase allowed to discard the log. The next write after a restore continues the restored numbering rather than colliding with it, and history and undo keep working; both are covered.

Verified: lifeboard 389 (+17), all packages green, offline e2e passes.