The condition→action abstraction (Pennington 1987: the mental model
with the highest error rates, and the one code text serves worst),
served on demand. Design per the research synthesis: thin caller-only
spine (thin slicing), closed question menu, guard text ON the edge
in words (information scent), glyphs always paired with text
(Reacher's 22% missed-icon failures), complexity-gated (Scanlan),
declared elision, both directions (Green), honest footer.
- /api/why?id|qn&dir=up|down: callers (or callees) with the
SYNTACTIC guard chain around each call site — enclosing
if/else/switch-case/loop/ternary/catch conditions, outermost
first, else-arm negation detected — extracted by parsing the few
caller files live with the embedded tree-sitter grammars from the
call-site line the CALLS edges already carry. Zero indexing cost;
works on every existing index. Per-request parse cache; 2 MB file
cap; unparseable sources reported as guards_unavailable, never
guessed.
- /api/trace&guards=1: A-to-B paths gain per-hop guard chips -
'reachable in 5 hops' becomes 'reachable when ...' (the exact gap
Reacher's users hit: they hand-derived conditionals).
- Symbol page: 'When does this run?' tree - guard chips (amber
unless / blue when), loop marker, unguarded honestly labeled,
per-caller upward expansion, direction toggle, single-line answer
when every call site is unguarded, footer stating guards are
syntactic and dispatch/events are invisible.
- Trace results in Flows render the same chips per hop.
Tests: nested-if chain outermost-first + else-arm negation + loop
flag + downward direction + callsite helper on a real temp-dir C
file (C); /api/why route wiring; formatGuard/chain + the
complexity gate (vitest). Trap fixed en route: the extension table
keys WITH the dot ('.c'), not 'c'.
Signed-off-by: Martin Vogel <martin.vogel.tech@gmail.com>
Martin Vogel
2df92078f9