bug: single-quoted strings inside `$(...)` lose embedded double quotes

[chaliy]

Problem

When a single-quoted string containing double quotes is used inside a command substitution $(...), the double quotes are stripped from the output. This breaks all JSON handling in pipe chains inside $(...).

Direct execution works correctly. The bug is in how the parser/expander handles single-quoted content within command substitution.

Reproduction

# Direct — correct:
echo '{"a":1}'
# Output: {"a":1}

# In command substitution — WRONG:
x="$(echo '{"a":1}')"
echo "${x}"
# Expected: {"a":1}
# Actual:   {a:1}

Impact

This is critical for any framework that processes JSON in bash. wedow/harness uses this pattern pervasively:

# Harness hook pipeline — every hook does this:
payload="$(cat)"
tools="$(echo "${tools}" | jq --argjson s '{"name":"bash"}' '. + [$s]')"
#                                          ^^^^^^^^^^^^^^^^^
#                                          quotes stripped → jq gets invalid input → empty output

Workaround: assign the JSON to a variable first, then use the variable:

# This works:
json_str='{"a":1}'
x="$(echo "${json_str}")"
echo "${x}"
# Output: {"a":1}

Test cases

# Basic: single quotes with embedded double quotes in $()
x="$(echo '{"key":"value"}')"
echo "${x}"
# Expected: {"key":"value"}

# Pipe chain in $()
result="$(echo '{"a":1}' | jq '.')"
echo "${result}"
# Expected: {
#   "a": 1
# }

# Multiple levels of quoting
y="$(echo 'say "hello" please')"
echo "${y}"
# Expected: say "hello" please

# Nested command substitution
z="$(echo "inner: $(echo '{"b":2}')")"
echo "${z}"
# Expected: inner: {"b":2}

# Backtick form (should match)
w="$(echo '"quoted"')"
echo "${w}"
# Expected: "quoted"

# Single quotes without double quotes — should be fine
v="$(echo 'no quotes here')"
echo "${v}"
# Expected: no quotes here