[lucidprogrammer]

Adds a new workspace under v2/, beside the current crates, which this change does not touch. Nothing that builds from crates/ changes; the root Cargo.toml and Cargo.lock are untouched.

What is in it

• v2/contextdb: the library. Tables with typed columns, a primary key, NOT NULL, UNIQUE, DEFAULT and indexes; INSERT, UPDATE, DELETE and SELECT over one table; transactions; one process writing a store while any number of other processes read it; a memory limit that holds. A store is one folder. Statements this version does not run yet (joins, vector search, relationships, sync clauses and others) are refused and change nothing.
• v2/contextdb-cli: the contextdb shell for a store, read-only by default, --write to write.
• v2/redb: the storage library. The first commit is upstream redb 4.1.0, source, tests and examples, unchanged. The second commit holds the changes, listed in v2/redb/README.md: a file its writer holds can be opened for reading at the newest whole commit, pages a reader still needs are not reused, and a page's checksum is checked when it is read.
• .github/workflows/check.yml: format, lint with warnings denied, tests on Linux and macOS, the storage library's own tests, a build on Rust 1.89, and two ceilings (shipped lines at most 150,000, tests at most 1,000). The existing workflow gains two paths-ignore lines so that a change touching only v2/ does not start it.

Commits

• 2c9a26956 storage: add redb 4.1.0 upstream source with tests and examples. 71 files, upstream unchanged; it is built from the next commit on, which adds it to the v2 workspace.
• bde61bdb7 contextdb: add v2 library and shell with typed columns, transactions, and concurrent access. 94 files.

Measured at this commit

By v2/numbers.sh: a release build on a 16-core AMD Ryzen 9 9955HX with 64 GB of memory and an NVMe drive, with nothing else running.

20,000 rows of 1.6 KB, one commit per row	17.2 s to insert, 60.3 MiB on disk
COUNT(*) of those rows	0.026 ms, no row read
Open that store after a clean close	0.6 ms
One million rows under a 64 MiB limit	loaded in 11.9 s, scanned in 246 ms; peak 13.4 MiB allocated, 18.0 MiB resident
First build of a program that embeds the library	5 s, 46 packages, a 2.7 MiB program
Fresh clone to a green cargo test	2.1 min
Shipped lines; tests	7,369; 87 tests and 11 SQL script files

Verification

• Every command of check.yml as written, on bde61bdb7, plus a cross-compiled lint for aarch64-apple-darwin: all pass. 87 of 87 tests; the storage library's 200 (upstream's 196 and 4 for the changes).
• GitHub Actions on bde61bdb7, new check: https://github.com/context-graph-ai/contextdb/actions/runs/42899137172 — green, 4 jobs (lint, tests on Linux, tests on macOS for the first time, Rust 1.89), 7 min (20:50–20:57 UTC).
• GitHub Actions on bde61bdb7, existing workflow, which runs here because its file changes: https://github.com/context-graph-ai/contextdb/actions/runs/42899137277 — green, 110 jobs passed, 1 skipped, 73 min (20:50–22:03 UTC).
• Two commits on dev 17b935c; reviewed by a second model family (SHIP).

Known and stated in the README

• After a writer is killed, readers open at once; the next writer first runs the storage library's repair, which reads every page in use (about half a second per GiB from a cold disk). An open after a clean close is under a millisecond.
• The smallest memory limit that opens a store is 9 MiB.
• A memory limit set inside a transaction takes effect at once and is not undone by a rollback.