[frankmcsherry]

The join fragments of #1085, held apart from the core language as a separate, opt-in step from surface text to plain DDP. A draft, for comparison with #1085; both are spikes.

How it differs from #1085

	#1085	This draft
Core lexer, parser, syntax tree, lowering, printers	*, [, ] tokens, the name( rule, Expr::Fragment, a lowering call, a printer arm (+44 lines)	master-next's, except lambda_in becomes crate-visible (+1/−1)
Fragment code	parse/pipe/fragment.rs, 480 lines, extending the core parser	src/surface.rs, 672 lines: its own scanner, a small printer for the generated text, surface positions
Tests	26 tests, 477 lines	8 tests, 215 lines
Tools	always on	ddir-plan --fragments, server load … --fragments; everything else reads plain DDP
Total against master-next	+1,001/−4	+933/−24

How it works

• surface::expand(text) replaces each fragment's source range with plain DDP and leaves every other byte unchanged; comments inside a fragment are copied to the start of its replacement.
• The core parser then reads the result. No fragment token, parser rule, syntax-tree node or lowering hook exists in the core.
• Errors keep their messages, prefixed with the line and column in the surface text.
• The expanded text is ordinary DDP an author can read, save and load without the flag.

The expansion is #1085's: written join order, key-slot reads, direct first joins, each test as a plain filter at its earliest join, variants through enlist unweave, and constant later keys rejected.

Checks

• All 47 valid fragment programs from DDIR: join fragments, a(x, y) * b(y, z), an experimental surface form (spike) #1085's tests, the eight spike programs, the demux and six placement examples give byte-identical plans to DDIR: join fragments, a(x, y) * b(y, z), an experimental surface form (spike) #1085 at the lowered and final stages (94 plans); the 35 rejected programs keep their errors.
• cargo test --release -p interactive -p ddir-server: 354 passed, 9 ignored.
• SCC, the access session, the authored LDBC fixture checker for IC3, IS6, BI11, BI14 and IC13, and the resolver match, several through raw fragment text and load --fragments.
• Coverage dropped from DDIR: join fragments, a(x, y) * b(y, z), an experimental surface form (spike) #1085's suite: dedicated tests for nested variants, the open-Result construction limit, string and list runtime cases, and printer round trips. Their programs still take part in the plan comparison.

Not intended to land as is.

Implemented by GPT-6 Sol (Codex); reviewed, tested and opened by Claude Code.

🤖 Generated with Claude Code

https://claude.ai/code/session_01H6wB4H99TLw4tqu4x48pXL