Add streaming SQLite snapshot installation

[findolor]

Chained PRs

1. Vendor sqlite-wasm-rs 0.3.0 #33 — vendor sqlite-wasm-rs 0.3.0.
2. Harden and extend sqlite-wasm-rs OPFS #34 — harden and extend the WASM/OPFS layer.
3. This PR: implement generic streaming snapshot installation and coordinated shutdown.

Motivation

Importing a large SQL dump in application code creates avoidable startup work, large transient allocations, and repeated application/worker crossings. Consumers need an application-agnostic way to install an authenticated SQLite snapshot safely across multiple tabs.

Implementation

• Adds installSnapshot(url, compression, sha256, uncompressedSize) with raw and gzip streaming.
• Streams response bytes through the database worker directly into an OPFS staging slot.
• Verifies exact size, SHA-256, SQLite structure, and PRAGMA quick_check before activation.
• Activates through staging/backup paths and restores the previous database on failure.
• Coalesces identical installs while preserving independent waiters.
• Coordinates leader/follower installs across tabs with explicit cancellation messages.
• Adds asynchronous await db.close(), followed by db.free().

Multi-tab shutdown contract

Every close performs an explicit coordinator shutdown handshake:

1. stop admitting new forwarded query, batch, and snapshot work;
2. authoritatively reject new forwarded requests;
3. drain or settle all already-accepted work;
4. acknowledge shutdown;
5. terminate workers and release OPFS ownership.

Snapshot cancellation is separately acknowledged and fenced immediately before activation. The caller never receives a cancellation/timeout failure followed by a hidden successful activation. Cancel-before-request ordering is tombstoned with bounded expiry, last-waiter cancellation does not absorb successor jobs, and leader close cannot strand follower-owned work.

Safety

• Existing databases survive download, digest, validation, cancellation, timeout, and activation failures.
• Corruption beyond the first SQLite page is caught before activation.
• Size/path inputs are checked without imposing snapshot-only path limits on ordinary database opens.
• Close/wipe races cannot resurrect a worker.
• Shutdown owns no application schema, Raindex manifest, contract, or RPC logic.

Review-loop fixes

Codex review drove fixes for recovery ordering, stream cancellation, leader loss, install coalescing, safe integer/path bounds, terminal close semantics, follower detach, cancellation acknowledgement, finalization fences, bounded cancel tombstones, successor-job ordering, leader/follower close interleavings, and explicit coordinator draining. The teammate review-loop skill was removed after verification at the user's request.

Verification

• sqlite-web-core Chrome WASM: 120/120
• public sqlite-web Chrome WASM: 42/42
• browser snapshot/shutdown integration: 13/13
• workspace wasm32 check passed
• Svelte check: 0 errors, 0 warnings
• formatting and diff checks passed

The browser regression suite covers raw/gzip install, digest/corruption preservation, oversize cancellation, two-client coalescing, close/wipe races, zero-yield install+close, follower cancellation, finalization cancellation, leader close with coalesced/follower-only work, and OPFS reopen handoff.

Downstream

Raindex integration: rainlanguage/raindex#2872, #2873, and #2871. The SQLite Web package must be released and Raindex's dependency version bumped before standalone runtime use.

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[findolor]

Warning

This pull request is not mergeable via GitHub because a downstack PR is open. Once all requirements are satisfied, merge this PR as a stack on Graphite.
Learn more

• Add streaming SQLite snapshot installation #32 👈 (View in Graphite)
• Harden and extend sqlite-wasm-rs OPFS #34
• Vendor sqlite-wasm-rs 0.3.0 #33
• main

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[findolor]

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