[Bug]: Suppression scanners lose enclosing nested case state

[ben-ranford]

Summary

The suppression scanners use one case mode per command frame. A nested case command replaces the outer case state; its terminator clears that state, so a later outer case-pattern closer is mistaken for the enclosing command-substitution closer. A genuine adjacent comment is missed.

Review evidence: #1650 (comment).

Reproduction steps

Run this shell source in zsh, then feed its full contents and a changed-line patch for line2 through tracker scanPatch. The review also identifies the corresponding transitions in the local and trusted workflow AWK scanners; verify parity during the fix.

v=$(case y in x) case z in z) :;; esac;;
y)#nolint
printf hi;; esac)
printf %s "$v"

Expected behavior

The shell prints hi. Line2 is a real comment and requires metadata plus a tracking record from each scanner.

Actual behavior

The tracker returns0records after the marker is given valid metadata. The inner case overwrites the scalar mode; the inner esac clears it instead of restoring the outer case. This is separate from ordinary-word esac handling being corrected in PR1650.

Logs and output

zsh parse exit: 0
zsh execution exit: 0
zsh stdout: hi
tracker expected records: 1
tracker actual records: 0

Proposed scope and acceptance criteria

Targetv1.9.0, medium coordinated grammar work. Recursive case syntax needs a per-command-frame stack and an AWK serialization design; one saved outer mode does not support recursion. PR1650's bounded operator/expansion correction does not add this grammar.

• Preserve enclosing case modes at two or more nested case levels; do not use one global saved mode.
• Detect genuine comments in inner and later outer patterns, with and without optional pattern parentheses.
• Keep the final hash suffix after the enclosing substitution literal.
• Cover same-line, multiline and full-file state seeding before changed hunks in tracker, local checker and trusted workflow verifier.
• Define stack serialization and restoration across command substitutions, subshells and case-arm transitions.
• Preserve quoted/escaped words, arithmetic/parameter exclusions, source content, metadata and fingerprints.
• Record bounded runtime and version evidence, plus failing-before/passing-after tests in all three scanners.

Version / commit

Reviewed3650a227b39e13eb76f3fd3051d2e7829fb077c7; reproduced5971cbacb5818e9163c355e81175b14bf2149721.

Environment

macOS with bundled Bash/sh and zsh, Node.js. The exact snippets below parse and print hi in zsh; bundled older Bash/sh reject these unparenthesized case-in-substitution forms. Do not generalize this evidence to all shell versions. Tracker scanPatch uses a read-only mocked full-file API with a changed-line patch; no external issue writes occur in the reproduction.