Most AI coding context generators have a hidden design flaw: they truncate long files sequentially from line 1 downward until they hit a token budget limit.
If a file has 1,200 lines and your budget allows 400 lines, the model receives lines 1 to 400. Everything from line 401 to 1200 vanishes.
In production codebases, this is fatal:
- Top: imports and constants
- Middle: core logic and helper functions
- Bottom: exported interfaces, route registrations, module.exports, and lifecycle bindings
When the agent cannot see module.exports or class registrations at the bottom, it assumes they do not exist and generates duplicate or broken code.
The Even-Span Sampling Methodology
To solve this without blowing the token budget, TokenCap implements even-span distribution in src/pack/evenSpan.js.
The algorithm divides the file into balanced intervals and samples structural slices while preserving AST function signatures:
// src/pack/evenSpan.js overview
function computeEvenSpans(lineCount, maxLines, anchorPoints) {
// Guarantees head imports, core anchor blocks, and tail exports
// are represented proportionally within the allocated budget.
}
Instead of:
Lines 1 - 350: Captured
Lines 351 - 1200: [TRUNCATED]
Even-span provides:
Lines 1 - 80: Header, configuration, types
... [140 lines folded] ...
Lines 220 - 310: Core logic and targeted symbols
... [290 lines folded] ...
Lines 600 - 680: Lifecycle handlers and bottom exports
Every span boundary snaps cleanly to structural declaration boundaries rather than slicing mid-statement.
Run tokencap make to inspect how your large files are budgeted.
Read more at tokencap.vansharora.app
Top comments (2)
Bottom truncation definitely burns agents on route registries and export tables. The trickier failure mode with discontinuous folds is the downstream edit step. If an agent tries to output a targeted string replacement or diff against code with folded intervals, it often anchors its search block right across the fold boundary unless the folding markers explicitly include the omitted line numbers. Keeping the original line offsets intact in the preview is what stops the patch tool from blowing up on the next turn.
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