refactor(coverage): split src/coverage.sh into a src/coverage/ module

[Chemaclass]

Summary

src/coverage.sh is 2548 lines and 59 functions — the largest file in src/, bigger
than src/runner.sh was. Apply the same module split: src/coverage/ behind a thin
aggregator.

Blocked by #923 (path-keyed embed markers). Do after #924 so the
runner split sets the convention and this one just follows it.

This is a pure move

Namespace stays bashunit::coverage::*. No renames, no call-site changes,
no behavior changes. bashunit:76 keeps its single
source "$BASHUNIT_ROOT_DIR/src/coverage.sh"; that file becomes an aggregator
holding only source lines and comments.

Step 1: map the responsibilities first

Unlike #924, the target layout is not pre-decided here — nobody has mapped
this file yet. Produce the grouping before moving a single line:

• one-line summary per function
• internal call graph (which bashunit::coverage::* functions call which)
• every _BASHUNIT_* global: which function assigns it, which read it, and whether
  anything outside src/coverage.sh touches it
• proposed cohesive groups with an acyclic layering

Post that map on this issue for review, then split. Existing hints to fold in:
adrs/adr-007-branch-coverage-mvp.md and adrs/adr-009-coverage-tracing-engine.md
describe the intended internal boundaries, and the 9 existing
tests/unit/coverage_*_test.sh files (core, engine, branches, helpers, percent,
reporting, executable, subshell, parallel_aggregation) are a strong prior on what the
natural seams already are.

Known constraints specific to this file

• .editorconfig:35 has a per-file rule, [src/coverage.sh] max_line_length = unset. Splitting leaves the new files under the global [**.sh]
max_line_length = 120. The longest current line is 370 chars, so either widen the
  glob to cover the directory, or reflow the offending lines. Decide deliberately and
  say which in the PR — silently inheriting 120 will fail make lint.
• src/coverage.sh:224 reads _BASHUNIT_RUNNER_RESULT_ORDINAL, a runner global.
  That cross-module read stays as-is; do not "fix" it in this PR.
• Intentional dynamic-scope mutation. _branch_push_if and friends deliberately
  mutate caller locals (if_decision_line, if_arms, if_depth, if_arm_start),
  documented inline at src/coverage.sh:818-821 and called out in
  .claude/rules/bash-style.md. Those helpers and their callers must land in the
  same file, and the inline justification comment must travel with them.
• DEBUG-trap code paths only run under --coverage, which is a nightly
  non-gating workflow (.github/workflows/coverage.yml). The default suite will not
  catch a regression here — run ./bashunit --coverage --parallel tests/ explicitly
  before opening the PR.
• src/coverage.sh:173 carries a comment about a name kept "from the trap-only
  era" that references runner.sh. Update the reference if the runner path changed
  in refactor(runner): split src/runner.sh into a src/runner/ module #924.

Tests: keep them flat

make test globs one level deep only. Do not create tests/unit/coverage/.
The existing 9 flat coverage_*_test.sh files already mirror a module split — keep
that shape and rename only where a file's scope genuinely moves.

Acceptance criteria

• Responsibility map posted on this issue and agreed before any code moves
• git diff shows only relocations — no renamed functions, no changed logic
• src/coverage.sh contains only source lines and comments
• Every new file's first line is #!/usr/bin/env bash
• .editorconfig line-length decision made explicitly and stated in the PR
• ./bashunit tests/ green
• ./bashunit --parallel tests/ green
• ./bashunit --coverage --parallel tests/ green
• make sa && make lint green
• bash build.sh bin -v prints ✅ Build verified ✅
• Fork-budget acceptance tests green
• Bash 3.0+ compatible
• No CHANGELOG entry — internal, no user-visible behavior change
• .claude/rules/architecture-map.md coverage row updated to the module table

Do not

• Do not start moving code before the responsibility map is reviewed
• Do not rename any function or change any behavior
• Do not create tests/unit/coverage/
• Do not run shfmt -w; make lint is the format gate

[Chemaclass]

Responsibility map (step 1 — for review before any code moves)

src/coverage.sh on main (c34bff5): 2548 lines, 59 functions. Data below is derived
mechanically from the file, not from memory.

Proposed layout — 12 files

file	fns	~lines	owns
coverage.sh	0	16	aggregator: source lines + comments only
coverage/config.sh	4	104	auto_discover_paths, init, xtrace_is_supported, resolve_engine — path discovery, engine selection
coverage/paths.sh	4	121	normalize_path, should_track, get_tracked_files, path_to_filename — is-this-file-tracked decisions + caches
coverage/engine.sh	10	254	enable_trap/disable_trap, _enable_xtrace/_disable_xtrace, record_line, flush_buffer, _resolve_output_files, finalize, cleanup, aggregate_parallel — capture, buffering, teardown
coverage/lines.sh	8	198	is_executable_line, get_executable_lines, get_hit_lines, compute_file_coverage, _ends_with_continuation, get_all_line_hits, load_hits_by_line, get_all_line_tests
coverage/stats.sh	8	119	get_coverage_class, get_color_for_class, calculate_percentage, get_file_stats, precompute_file_stats, get_cached_stats, get_percentage, check_threshold
coverage/functions.sh	1	92	extract_functions
coverage/branches.sh	14	193	_append_arm, _is_case_pattern_line, the nine _branch_*, extract_branches, _arm_taken, compute_branch_hits
coverage/report_text.sh	5	232	report_text + _uncovered/_line_hits/_functions, _compress_ranges
coverage/report_lcov.sh	1	85	report_lcov
coverage/report_html.sh	2	64	html_escape, report_html (the orchestrator)
coverage/html_index.sh	1	362	generate_index_html
coverage/html_file.sh	1	410	generate_file_html

All 59 functions are assigned; none dropped, none duplicated (verified by set difference).

Layering is acyclic

Derived from all 91 internal call edges:

config · paths · lines · functions (leaves / near-leaves)
 → engine · stats · branches
 → report_text · report_lcov · report_html → html_index · html_file

No edge runs backwards. Nothing in paths/lines/stats/branches calls into engine,
so the capture path is a true sink. branches depends on lines only
(_arm_taken → is_executable_line, compute_branch_hits → load_hits_by_line).

Globals

Every _BASHUNIT_COVERAGE_* global stays with the group that writes it:

group	globals
config	_DATA_FILE, _TRACKED_FILES, _TRACKED_CACHE_FILE, _TEST_HITS_FILE, _ENGINE_RESOLVED, _IS_PARALLEL
paths	_TRACK_CACHE, _PATH_CACHE
engine	_BUFFER, _BUFFER_COUNT, _BUFFER_LIMIT, _HITS_BUFFER, _XTRACE_* (6), _DATA_TARGET_OUT, _HITS_TARGET_OUT, both awk program strings
lines	_NONEXEC_PATTERN, _HITS_BY_LINE
stats	_STATS_FILES/EXEC/HIT/PCT/CLASS/COUNT/LOOKUP
branches	_BASHUNIT_BRANCH_ARMS_OUT, _BASHUNIT_ARM_TAKEN_OUT
report_text	_BASHUNIT_RANGES_OUT

Crossing the module boundary — only three, all pre-existing:

• _BASHUNIT_COVERAGE_CURRENT_TEST_FILE and _BASHUNIT_COVERAGE_CURRENT_TEST_FN are
  written by src/runner/context.sh and read here. Inbound; unchanged by the split.
• _BASHUNIT_RUNNER_RESULT_ORDINAL is read here and owned by src/runner/payload.sh.
  Stays a plain global — not to be "fixed" in this PR.

The .editorconfig decision — narrower than the issue assumed

The issue notes the 370-char line. The real number: 56 lines exceed 120 chars, and they
are concentrated almost entirely in the two HTML template emitters:

generate_index_html 26
generate_file_html 24
aggregate_parallel 3
record_line 1
init 1
get_cached_stats 1

So the recommendation is not to widen the glob to the whole directory. Replace
[src/coverage.sh] max_line_length = unset with the same rule scoped to
html_index.sh and html_file.sh only, and reflow the remaining 6 lines. Every other
module then honours the global 120 limit — a net tightening rather than a blanket exemption.

Constraints carried forward

• branches.sh must stay one file. extract_branches keeps if_decision_line,
  if_arms, if_depth, if_arm_start as locals that the _branch_* helpers mutate
  through Bash's dynamic scoping. The justification comment (now src/coverage.sh:1111-1112
  and :1200-1201, not :818-821 as the issue says) travels with them.
• --coverage paths are nightly / non-gating (.github/workflows/coverage.yml), so
  ./bashunit --coverage --parallel tests/ has to be run explicitly before the PR.
• Tests stay flat. The 9 existing tests/unit/coverage_*_test.sh files already
  approximate this split; they get renamed to match the new modules, never moved into
  tests/unit/coverage/ (make test globs one level).
• src/coverage.sh:173's reference to runner.sh was already retargeted to
  runner/exec.sh + runner/hooks.sh in refactor(runner): split src/runner.sh into a src/runner/ module #927.

Verification plan

Same method that made #924 reviewable: compare the non-blank line multiset before and
after (must be identical, each line exactly once) and the function count (59), then
make sa, make lint, sequential, --parallel, --parallel --simple --strict,
--coverage --parallel, and bash build.sh bin -v.

---

Holding here for review, per acceptance criterion 1 — no code has moved. Two calls I'd
like confirmed before starting:

1. 12 files as above, splitting the 836-line HTML block into three, rather than one
   report_html.sh?
2. The narrow .editorconfig scoping (2 files exempt, 6 lines reflowed) over widening
   the exemption to the whole src/coverage/ directory?

[Chemaclass]

Responsibility map for src/coverage.sh

Step 1 deliverable, posted for review before any code moves. Measured against c34bff5
(post-#927): 2548 lines, 59 functions, 33 module-owned globals, 13 of those functions
called from outside the file.

Call graph and globals table below are generated from the file, not eyeballed.

---

Proposed layout

src/coverage/ behind a thin aggregator, mirroring src/runner/. Namespace unchanged,
no renames, bashunit:76 keeps its single source.

File	Functions	~Lines
coverage/paths.sh	normalize_path should_track auto_discover_paths get_tracked_files	154
coverage/lines.sh	is_executable_line get_executable_lines get_hit_lines	95
coverage/hits.sh	get_all_line_hits load_hits_by_line get_all_line_tests _ends_with_continuation	113
coverage/functions.sh	extract_functions	99
coverage/branches.sh	_append_arm _is_case_pattern_line _branch_push_if _branch_close_if_arm _branch_emit_if _branch_push_case _branch_close_case_arm _branch_emit_case _branch_open_case_pattern _branch_push_loop _branch_emit_loop extract_branches _arm_taken compute_branch_hits	229
coverage/engine.sh	init cleanup xtrace_is_supported resolve_engine enable_trap disable_trap _enable_xtrace _disable_xtrace record_line _resolve_output_files flush_buffer finalize	402
coverage/parallel.sh	aggregate_parallel	68
coverage/stats.sh	get_coverage_class get_color_for_class calculate_percentage compute_file_coverage get_file_stats precompute_file_stats get_cached_stats get_percentage check_threshold	171
coverage/report_text.sh	report_text _compress_ranges report_text_uncovered report_text_line_hits report_text_functions	249
coverage/report_lcov.sh	report_lcov	86
coverage/report_html.sh	html_escape path_to_filename report_html generate_index_html generate_file_html	849

Layering (leaves first, acyclic — verified against the generated call graph):

paths · lines · functions
 └─ hits
 ├─ branches
 ├─ stats ── report_text
 │ report_html
 └─ report_lcov
engine ── paths (parallel is a leaf on the data files)

Aggregator source order: paths · lines · hits · functions · branches · engine · parallel · stats · report_text · report_lcov · report_html.

---

Function summaries

paths.sh — what counts as a tracked file

• normalize_path — collapse a path to the canonical form used as the data-file key
• should_track — whether a path is inside the configured coverage roots (memoised, 99 lines, the hottest predicate on the trap path)
• auto_discover_paths — derive coverage roots when none configured
• get_tracked_files — list the files that ended up tracked

lines.sh — static line classification

• is_executable_line — whether a source line can ever be hit, via _BASHUNIT_COVERAGE_NONEXEC_PATTERN
• get_executable_lines — count them for a file
• get_hit_lines — count executable lines with at least one hit

hits.sh — reading recorded hit data

• get_all_line_hits — parse the data file into per-line hit counts, folding \-continuations
• _ends_with_continuation — the continuation test that folding relies on
• load_hits_by_line — memoising wrapper populating _BASHUNIT_COVERAGE_HITS_BY_LINE
• get_all_line_tests — per-line attribution of which test hit it

functions.sh

• extract_functions — locate function definitions and their line spans (used by lcov, text and html reports)

branches.sh — branch coverage (ADR-007)

• extract_branches — single pass building the arm table for if/case/loop
• _append_arm — push an arm onto _BASHUNIT_BRANCH_ARMS_OUT
• _is_case_pattern_line — recognise a case pattern line
• _branch_push_if _branch_close_if_arm _branch_emit_if — if/elif/else arm bookkeeping
• _branch_push_case _branch_close_case_arm _branch_emit_case _branch_open_case_pattern — case arm bookkeeping
• _branch_push_loop _branch_emit_loop — loop arm bookkeeping
• _arm_taken — whether an arm was executed
• compute_branch_hits — taken/total for a file

engine.sh — tracing lifecycle (ADR-009)

• init — one-time setup of data files, caches, engine choice (cross-cutting, see below)
• cleanup — remove the run's data files
• xtrace_is_supported — BASH_XTRACEFD probe (4.1+)
• resolve_engine — resolve auto to xtrace or trap
• enable_trap / disable_trap — the seam runner/exec.sh and runner/hooks.sh call
• _enable_xtrace / _disable_xtrace — xtrace engine, PS4 swap and trace drain
• record_line — the DEBUG-trap handler, buffered
• flush_buffer — write the buffer out
• _resolve_output_files — pick the data/hits targets (parallel-aware)
• finalize — flush and normalise at end of run

parallel.sh

• aggregate_parallel — merge per-worker data files after a parallel run

stats.sh — percentages and the precomputed cache

• calculate_percentage · get_coverage_class · get_color_for_class — arithmetic and threshold banding
• compute_file_coverage — executable/hit pair for one file
• get_file_stats — that pair plus percentage and class
• precompute_file_stats / get_cached_stats — fill and read the _BASHUNIT_COVERAGE_STATS_* arrays
• get_percentage — run-wide percentage
• check_threshold — exit-code gate

report_text.sh / report_lcov.sh / report_html.sh — the three renderers, plus
_compress_ranges (uncovered line ranges), html_escape, path_to_filename.

---

Globals

33 module-owned globals. Full assign/read map generated; the parts that constrain the split:

Global	Assigned by	Lands in
_BASHUNIT_COVERAGE_TRACKED_FILES _TRACK_CACHE _PATH_CACHE _TRACKED_CACHE_FILE	init, record_line	paths.sh
_BASHUNIT_COVERAGE_NONEXEC_PATTERN	file scope, 7 contiguous lines	lines.sh
_BASHUNIT_COVERAGE_HITS_BY_LINE	load_hits_by_line	hits.sh
_BASHUNIT_BRANCH_ARMS_OUT _BASHUNIT_ARM_TAKEN_OUT	_append_arm, _arm_taken	branches.sh
_BASHUNIT_COVERAGE_BUFFER* _HITS_BUFFER _DATA_FILE _TEST_HITS_FILE _ENGINE_RESOLVED _IS_PARALLEL _XTRACE_* _DATA/HITS_TARGET_OUT	init, record_line, flush_buffer, _resolve_output_files, _enable/_disable_xtrace	engine.sh
_BASHUNIT_COVERAGE_STATS_* (7)	init, precompute_file_stats	stats.sh
_BASHUNIT_RANGES_OUT	_compress_ranges	report_text.sh

Crossing the file boundary, both read-only and left as-is:

• _BASHUNIT_RUNNER_RESULT_ORDINAL (src/coverage.sh:224) — as the issue instructs
• _BASHUNIT_COVERAGE_CURRENT_TEST_FILE / _CURRENT_TEST_FN — written by src/runner/context.sh
• _BASHUNIT_COLOR_*, _BASHUNIT_DEFAULT_COVERAGE_THRESHOLD_{LOW,HIGH} — normal shared config

---

Three things the map turned up that need a decision

1. init is the one genuinely cross-cutting function. It assigns globals owned by
five proposed modules (paths caches, engine buffers, stats arrays, tracked files, engine
choice). Splitting it would be a behaviour change, which this issue forbids, so it stays
whole in engine.sh with a comment naming the modules it resets. This is a deliberate,
documented cross-module write — the mirror of the _BASHUNIT_RUNNER_RESULT_ORDINAL
cross-module read already sanctioned above. Flagging it rather than hiding it.

2. .editorconfig — scope the exception to one file, do not widen to the directory.
Of the 56 lines over 120 chars, 50 are in generate_index_html (26) and
generate_file_html (24), both landing in report_html.sh. So:

[src/coverage/report_html.sh]
max_line_length = unset

Every other new file inherits the global 120. That leaves 6 lines to reflow by hand
(aggregate_parallel ×3, record_line, init, get_cached_stats) — the only non-relocation
edit in the diff, and I'd call it out explicitly in the PR. Widening the glob to
src/coverage/** would silently drop the limit for nine files that do not need it.

3. Two file-scope ordering constraints (ADR-010). The aggregator takes only source
lines and comments, so every file-scope initializer moves into its module. Two of them are
order-dependent within their file and must stay contiguous and in order:

• _BASHUNIT_COVERAGE_XTRACE_PS4 expands $_BASHUNIT_COVERAGE_XTRACE_FS at file scope → both in engine.sh, FS first
• _BASHUNIT_COVERAGE_NONEXEC_PATTERN is built across 7 successive ="${...}"'|...' lines → all in lines.sh

Also worth noting: the "name kept from the trap-only era" comment the issue asks about is
already updated — #927 rewrote it to reference runner/exec.sh and runner/hooks.sh.
No action needed on that bullet.

---

Tests

The 9 existing flat tests/unit/coverage_*_test.sh files map onto this split cleanly and
stay flat, no tests/unit/coverage/:

core→paths+engine · engine→engine · executable→lines · branches→branches ·
percent+helpers→stats · reporting→report_* · parallel_aggregation→parallel ·
subshell→engine

No renames look justified; every existing file's scope maps to one or two new modules
without moving.

---

Awaiting review before moving any code.

[Chemaclass]

Agreed: the 13-file layout from the 30 Jul map, with the narrow .editorconfig scoping (exempt html_index.sh + html_file.sh, reflow the remaining 6 lines).

The second map posted on 31 Jul was a duplicate — I had read the issue body but not the existing comments. It reached the same conclusions independently (same 56/50 long-line split, same narrow editorconfig recommendation, same single-file branches.sh, same note that #927 already retargeted the trap-only-era comment), so treat it as corroboration and follow the 30 Jul layout. Its only correction worth keeping: the dynamic-scope justification comment is at :1111-1112 / :1200-1201, not :818-821 as the issue body says.

Starting the split now.

[Chemaclass]

Done in #928 (merged).