Add a prototype AGENTS.md file

FossilOrigin-Name: 3dd1181120b9910a96090b5b3cad5f0829fadeffeb6ffaad17031540a5749513

AGENTS.md

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+# AGENTS.md
+
+Guidance for AI coding agents working in this repository.
+
+## Project nature
+
+SQLite is a self-contained, serverless SQL database engine written in C. The
+source is **public domain** — no copyright or license header should ever be
+added to any file. The blessing comment that appears at the top of each source
+file is intentional and should be preserved unchanged.
+
+SQLite does not accept pull requests without prior agreement and/or
+accompanying legal paperwork that places the pull request in the public domain.
+However, the human SQLite developers will review a concise and well-written
+pull request as a proof-of-concept prior to reimplementing the changes
+themselves.
+
+SQLite does not (currently) accept agentic code.  However the project
+will accept agentic bug reports that include a reproducible test case.
+Patches or pull requests demonstrating a possible fix, for documentation
+purposes, are welcomed.
+
+SQLite uses the [Fossil](https://fossil-scm.org/) for version control,
+not Git.  The canonical repository is at <https://sqlite.org/src>.
+
+## Build
+
+The configure script uses [autosetup](https://msteveb.github.io/autosetup/),
+not GNU Autoconf.
+
+```bash
+apt install gcc make tcl-dev   # prerequisites (Debian/Ubuntu)
+
+./configure --dev              # debug build
+make sqlite3                   # CLI shell
+make sqlite3d                  # Debugging variant of the CLI shell
+make sqlite3.c                 # amalgamation (single-file distribution form)
+make testfixture               # test runner binary (requires tcl-dev)
+make tclextension-install      # install TCL extension before running tests
+```
+
+## Testing
+
+Tests are TCL scripts run through the `testfixture` enhanced interpreter.
+
+```bash
+# From the build directory:
+./testfixture test/main.test   # single test file
+test/testrunner.tcl            # quick suite
+test/testrunner.tcl full       # full suite
+test/testrunner.tcl fts5%      # pattern match
+
+# Check for failures:
+grep '!' testrunner.log
+```
+
+`make devtest` is the fastest way to run a representative subset. Always run
+at least `devtest` after any change to `src/`.
+
+## Architecture
+
+SQL text → **tokenizer** (`tokenize.c`) → **parser** (`parse.y` / Lemon) →
+**code generator** (`build.c`, `select.c`, `insert.c`, `update.c`, `delete.c`,
+`expr.c`) → **optimizer** (`where*.c`) → **VDBE** (`vdbe.c`) → **B-Tree**
+(`btree.c`) → **Pager** (`pager.c`) → **WAL** (`wal.c`) → **VFS**
+(`os_unix.c`, `os_win.c`).
+
+The master internal header is `src/sqliteInt.h`. Major subsystems have private
+headers: `vdbeInt.h`, `btreeInt.h`, `whereInt.h`. The public API is defined in
+`src/sqlite.h.in` (template) which generates `sqlite3.h`.
+
+## Do not edit generated files
+
+These files are produced by scripts and must not be edited by hand:
+
+| File | Regenerate with |
+|---|---|
+| `sqlite3.h` | `tool/mksqlite3h.tcl` |
+| `parse.c`, `parse.h` | build lemon (`tool/lemon.c`) then run on `src/parse.y` |
+| `opcodes.h` | `tool/mkopcodeh.tcl` (reads `src/vdbe.c`) |
+| `opcodes.c` | `tool/mkopcodec.tcl` (reads `opcodes.h`) |
+| `keywordhash.h` | `tool/mkkeywordhash.c` |
+| `pragma.h` | `tool/mkpragmatab.tcl` |
+| `sqlite3.c` | `tool/mksqlite3c.tcl` (the amalgamation) |
+
+Editing rules:
+- To add a PRAGMA: edit `tool/mkpragmatab.tcl`, then regenerate `pragma.h`.
+- To add a VDBE opcode: add the `case OP_Xxx:` handler in `src/vdbe.c`; the
+  opcode number and name are extracted automatically by `mkopcodeh.tcl`.
+- To change the SQL grammar: edit `src/parse.y`, not `parse.c`.
+
+## Coding conventions
+
+- C89/C99 compatible C only. No C++, no STL, no exceptions, no VLAs.
+- All memory allocation goes through `sqlite3Malloc` / `sqlite3_malloc64`
+  (never raw `malloc`). The `sqlite3MallocZero` variant zero-initializes.
+- Integer widths: use `i64` (`sqlite3_int64`) for 64-bit values, `u32`/`u64`
+  for unsigned. Avoid bare `long` or `int` for values that could exceed 2G.
+- Error propagation: functions return `SQLITE_OK` (0) on success and a
+  `SQLITE_*` error code on failure. Many routines also set `db->mallocFailed`
+  on OOM, allowing deferred error checking.
+- Assert liberally for invariants that must hold in correct code; use
+  `ALWAYS(x)` / `NEVER(x)` for conditions that are logically always
+  true/false but that the compiler cannot prove.
+
+## Extensions (`ext/`)
+
+Extensions are compiled separately from the core and are not part of the
+amalgamation by default (except where explicitly included). Major subsystems:
+
+- `ext/fts5/` — Full-Text Search 5 (current)
+- `ext/rtree/` — R-Tree spatial indexing
+- `ext/session/` — Changesets and sessions
+- `ext/recover/` — Database file recovery
+- `ext/misc/` — Single-file utility extensions (many included in the CLI)
+- `ext/qrf/` — Query Result Formatter utility library
+
+## Useful references
+
+- Architecture: <https://sqlite.org/arch.html>
+- File format: <https://sqlite.org/fileformat2.html>
+- VDBE opcodes: <https://sqlite.org/opcode.html>
+- Query planner: <https://sqlite.org/optoverview.html>
+- Lemon parser generator: <https://sqlite.org/doc/trunk/doc/lemon.html>
+- Compile-time options: <https://sqlite.org/compile.html>

manifest

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-D 2026-05-21T15:14:35.420
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 # Remove this line to create a well-formed Fossil manifest.

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