dangernoodle-io / breadboard / 26137798989

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fix(bb_openapi): stream the OpenAPI doc instead of materializing a 26+ KB tree (#279)

GET /api/openapi.json was crashing httpd workers on tight-stack boards
(ESP32-WROOM-32, tdongle-s3) once the route count grew past ~50 in the
v0.30 → v0.33 window. Symptom: TCP accepts, request delivered, server
closes connection without headers (handler aborted mid-response). Root
cause: bb_openapi_emit built the full JSON tree in a single cJSON
allocation, then bb_http_resp_send_json recursively walked it through
the chunked-encoding path — peak heap + recursive serialize stack
together exceeded the 6144-byte httpd worker budget on a now-26 KB
document. (B1-222)

Add `bb_openapi_emit_stream(req, meta)`: streams the document piece by
piece via bb_http_resp_send_chunk. Each operation's JSON tree is built,
serialized, and freed individually, so peak memory is bounded to one
operation (~1 KB) instead of the whole document (~26 KB). The platform
handler in bb_openapi_register switches to the streaming variant; the
existing tree-build `bb_openapi_emit` is preserved for tests and any
consumer that wants the full bb_json_t tree.

Validated on bench: bitaxe-650 returns the full 26882-byte spec in
162 ms, esp32-wroom32 returns 24875 bytes in 617 ms — both with no
httpd worker wedge. Five new host tests cover the streaming path
(produces valid doc, NULL-arg guards, servers/description fields,
default-fallbacks, multi-method paths) using an extended host
send_chunk stub that appends each chunk into the capture body. 887
host tests pass; bb_openapi_emit.c at 100% line + 100% branch coverage
(platform-impossible alloc-failure / send-error returns marked
LCOV_EXCL_BR_LINE to match the codebase's existing convention).

Drive-by: move `#define _POSIX_C_SOURCE 200112L` to the top of
bb_event_ring.c, before any include. glibc's features.h locks the
macro at the default once anything pulls it in transitively, so the
mid-file define produced "_POSIX_C_SOURCE redefined" warnings on eve... (continued)

1020 of 1020 branches covered (100.0%)

Branch coverage included in aggregate %.

70 of 70 new or added lines in 1 file covered. (100.0%)

1867 of 1867 relevant lines covered (100.0%)

965.33 hits per line