perf(local): quote SQL literals with a bash expansion, not a fork

[fujibee]

Picks up the work in #897, with credit to its author in the commit trailer.

The local send/inbox/history/watch path forked printf | sed to double single quotes at eight sites. Those are bash parameter expansions now, and the fork is gone from that path.

The idea and the eight sites are from #897. What changed is the shape.

Why the shape matters

Seven of the eight were written as ${v//\'/\'\'}, with the quote inline in the pattern.

bash 3.2 — which is /bin/bash on macOS, and what the macOS CI jobs run — keeps the backslash of a \' replacement. Measured on both:

	backslash form	quote-in-a-variable
bash 3.2.57	a\'\'b	a''b
bash 5.3.15	a''b	a''b

The difference is invisible on Linux, which is why the form reads as correct. It is also why the macOS jobs went red on #897.

So the quote is held in a variable at all eight — the shape _sqlite_sync_lit_into in sqlite-sync.sh already uses, and documents, for this exact reason.

The failure this change can have, and what stops it

An undefined quote variable is the dangerous one. ${v//​/} with an empty pattern returns the value unchanged, so quotes silently stop being doubled — on every bash, with no error.

Three of the seven files had no declaration in scope after a first mechanical pass. That is not a hypothetical: it was this change, before it was checked.

tests/test_local_quoting.bats counts substitutions against declarations per file, so it cannot pass unnoticed again.

Equivalence

Held equal to the forking form it replaces, on the inputs that matter to SQL quoting — quote alone, doubled, leading, trailing, newline, tab, backslash, backslash next to a quote, empty, and sed's and printf's own metacharacters — under the suite's own bash and under /bin/bash.

The second test skips with a reason when /bin/bash is 4+, rather than passing quietly while testing nothing.

Mutations

#	mutation	result
A	back to the backslash form	green on modern bash, red under /bin/bash — the failure #897 hit, reproduced
B	one declaration removed	red on the scope count

A is the one worth reading: it is exactly why this could not just be merged as proposed.

Ran

test_messaging 27, test_api 18, test_export 13, test_team 79, test_inbox 9, test_watch 22, test_storage 25, test_local_quoting 4 — 197 tests, 0 failures, on the committed branch.

End to end through the installed scripts: a message carrying a quote, doubled quotes and a backslash arrives byte-identical.

Not run locally: the full matrix. CI's job.

Scope

• The seven files perf: replace sed subprocess with bash-native SQL literal escaping (local send/inbox/history/watch path) #897 touches. sqlite-sync.sh is deliberately untouched — its remaining sites belong to separate work.
• The same forking form appears at 81 sites across 28 files in scripts/. This converts the 8 on the hot local path, not the rest; the remainder is a sweep with its own risk and its own measurement.