Add structured Bash command substitutions

IMPLEMENTATION_PLAN.md

@@ -258,10 +258,19 @@ priorities.
       unknown fields and always requires unparseable projections to be empty.
       The PowerShell manifest now owns all 310 entries and round-trips exactly;
       explicit false/null assertions remain opt-in and generator-preserved.
-- [ ] Deliver paired Bash and PowerShell `$()` substitution slices for all
-      locked executable value positions, including ordering, ancestry,
-      shell-specific cwd propagation, literal/escaped boundaries, dynamic
-      identities, fail-closed negatives, executable corpus, and Netclaw cases.
+- [x] Deliver the first Bash `$()` substitution slice for supported
+      simple-command arguments and redirect targets. Direct tests and corpus
+      entries pin multiple and nested ordering, exact ancestry/spans, isolated
+      cwd, decoded wrappers, literal boundaries, dynamic compatibility values,
+      depth limits, comment-safe delimiter scanning, and fail-closed command
+      identities, background lists, assignment prefixes, backticks, heredocs,
+      and malformed interiors.
+- [ ] Extend Bash substitution discovery to iterables and expanding heredoc
+      bodies, then add the corresponding Netclaw approval-matrix cases.
+- [ ] Deliver the PowerShell `$()` substitution slice for every locked value
+      and expression position, including current-scope state propagation,
+      literal boundaries, incomplete dynamic identities, executable corpus,
+      and Netclaw cases.
 - [ ] Deliver Bash `for ... in` and PowerShell `foreach` as the first two
       language-specific vertical slices, then extract only the shared analysis
       proven by both implementations.

SPEC.md

@@ -53,12 +53,11 @@ command can consume it.
 - Variable expansion. We mark dynamic tokens, never resolve them.
 - Function definitions, here-docs body extraction, complex parameter
   expansion (`${var//pattern/replacement}`), arithmetic expansion.
-- Command-substitution evaluation. `$(cmd)` and backtick `` `cmd` `` are
-  recognized at the lex level and collapsed into a single
-  `Kind=DynamicSkip, IsPath=false` arg per locked interpretation #2 (see
-  `openspec/changes/archive/.../v0.1-locked-interpretations`). The
-  surrounding clause stays parseable so hard-deny rules still fire on
-  visible parts.
+- Command-substitution evaluation. The library never executes a substitution
+  or claims its produced value is known. Stable v0.3 recursively discovers
+  commands inside supported Bash `$()` positions while retaining the authored
+  `Kind=DynamicSkip, IsPath=false` compatibility value. Legacy backticks and
+  incomplete executable interiors fail closed.
 - Performance tuning beyond "fast enough to invoke per shell call without
   noticeable latency" (~1ms per typical input).
 
@@ -966,7 +965,9 @@ quoted_string   := single-quoted | double-quoted
   immediately following a compound operator all collapse: they never
   yield an empty clause. The newline after a heredoc terminator likewise
   separates the heredoc's clause from what follows.
-- `\` followed by a newline is a line continuation (treat as whitespace).
+- `\` followed by a newline is removed before word-boundary analysis. It joins
+  adjacent fragments (`r\` + newline + `m` is the command name `rm`); actual
+  surrounding spaces still separate words.
 - Bash line comments (`#` at a word boundary through end-of-line) are
   whitespace-equivalent at the lexer level — they emit a Comment token
   for source fidelity but are filtered alongside Whitespace by the
@@ -982,10 +983,10 @@ quoted_string   := single-quoted | double-quoted
   NOT path-resolved. The parser carries the raw token (e.g. `&1`) on
   `Redirect.Target` and sets `Redirect.IsDynamicSkip = true`. This
   prevents `2>&1` from being incorrectly resolved to `<cwd>/&1`.
-- Function definitions, `case`/`esac`, C-style or implicit loops, arithmetic
-  execution, process substitution, and single-`&` background lists remain
-  unparseable in stable v0.3 because they can hide executable regions outside
-  the bounded grammar below.
+- Function definitions, assignment-prefix commands, `case`/`esac`, C-style or
+  implicit loops, arithmetic execution, process substitution, and single-`&`
+  background lists remain unparseable in stable v0.3 because they can hide
+  executable regions outside the bounded grammar below.
 
 ### v0.3 structured Bash grammar
 
@@ -1072,7 +1073,8 @@ The lexer produces tokens consumed by the parser. Token kinds:
   is flagged as a **statement separator**; the parser retains those
   tokens past `FilterSignificant` and splits clauses on them per §4. A
   pure space/tab run carries no flag and is discarded after splitting.
-- **CONTINUATION** — `\` + `\n`. Treated as whitespace.
+- **CONTINUATION** — `\` + `\n` (or `\r\n`). Removed before word-boundary
+  analysis; adjacent lexical fragments remain one authored word.
 - **OPAQUE_SUBSTITUTION** — `$(cmd)` or backtick `` `cmd` ``. The full
   substitution slice (including delimiters) becomes a single token.
   Boundary tracking handles nested same-kind regions, nested quotes,

openspec/changes/v0-3-structured-shell-analysis/tasks.md

@@ -32,9 +32,12 @@
 - [x] 3.8 Add tests proving existing parser inputs retain their v0.2 leaf and compatibility results, except for explicitly promoted v0.3 fail-closed cases.
 - [x] 3.9 Add corpus expectations for syntax shape, occurrences, roles, and completeness for existing constructs.
 - [ ] 3.10 Implement Bash `$()` discovery in supported argument words, redirect values, iterables, and expanding heredoc bodies; retain literal/escaped spellings and fail closed on command-name substitutions, legacy backticks, or incomplete interiors.
+  - [x] 3.10a Implement the simple-command argument and redirect-target slice, including comment-safe boundaries and fail-closed unsupported interiors.
 - [ ] 3.11 Implement PowerShell `$()` discovery in supported words, redirect values, foreach expressions, call-operator dynamic identities, standalone expression statements, double-quoted strings, and expandable here-strings; never invent invocation from standalone output, retain literal/escaped spellings, and fail closed on trailing command-style arguments, call-operator script blocks, or unsupported execution-bearing `@()` / `@{}` forms.
 - [ ] 3.12 Pin substitution parentage, authored sibling indices, innermost-first ordering, Bash-isolated versus PowerShell-current-scope state, unknown-state propagation, nesting/depth limits, and incomplete dynamic identities in direct tests.
+  - [x] 3.12a Pin the Bash argument/redirect slice, isolated cwd behavior, wrapper provenance, and the shared structural-depth budget.
 - [ ] 3.13 Promote ordinary, multiple, nested, iterator, redirect, quoted, escaped, stateful, malformed, and hidden-execution substitution cases into both executable corpora and the Netclaw approval matrix.
+  - [x] 3.13a Promote the Bash ordinary, multiple, nested, redirect, quoted, escaped, stateful, malformed, and hidden-execution cases into its executable corpus.
 
 ## 4. Explicit Redirect Semantics