fix: extend isMarkdownFilename across remaining session-start call sites

[breferrari]

Summary

• Closes Extend isMarkdownFilename across listMd() and brainIndex() in session-start.ts #88. PR fix: stop SessionStart from flashing Obsidian app on macOS, close ExperimentalWarning stderr leak (#83) #87 introduced the case-insensitive isMarkdownFilename helper for the new listMarkdownSources scanner but three pre-existing call sites in session-start.ts still used endsWith(".md") and a case-sensitive /\.md$/ strip. On NTFS/APFS (case-insensitive filesystems), a file saved as Note.MD or note.Md was silently dropped from the brain index, the active work section, and the vault file listing.
• The audit also caught two more in lib/session-start.ts:34, 35 inside formatActiveWork() — same module, same bug, same fix. Bundled per PR fix: stop SessionStart from flashing Obsidian app on macOS, close ExperimentalWarning stderr leak (#83) #87's "two bugs, one PR" precedent.

Sites changed

File	Line	Function	Before	After
session-start.ts	208	brainIndex() filter	e.name.endsWith(".md")	isMarkdownFilename(e.name)
session-start.ts	212	brainIndex() strip	f.replace(/\.md$/, "")	f.replace(/\.md$/i, "")
session-start.ts	258	listMd() filter	e.name.endsWith(".md")	isMarkdownFilename(e.name)
lib/session-start.ts	34	formatActiveWork() filter	f.endsWith(".md")	isMarkdownFilename(f)
lib/session-start.ts	35	formatActiveWork() strip	f.replace(/\.md$/, "")	f.replace(/\.md$/i, "")

isMarkdownFilename was already imported into session-start.ts at line 36 — no import shuffle.

Cross-platform behaviour

The change is pure-string filter and regex logic. No filesystem APIs touched.

Filesystem	Effect
NTFS (Windows) — case-insensitive	A Note.MD saved by a different tool was silently dropped; now listed. No regression for lowercase files.
APFS default (macOS) — case-insensitive	Same as NTFS.
ext4 (Linux) — case-sensitive	Note.md and Note.MD are distinct files; both are now listed instead of just lowercase. Cosmetic duplicate after extension strip; matches PR #87's precedent (isMarkdownFilename already accepts both).
APFS case-sensitive (macOS, opt-in)	Same as ext4.

The new unit test passes synthetic filenames (no real FS) so behaviour is identical on every OS. Existing CI matrix exercises this on ubuntu / macos / windows × Node 22 / 24.

Test coverage

• New test in formatActiveWork's describe block (session-start.test.ts:73–80): locks .MD/.Md/.md all pass the filter, extension stripped correctly, non-markdown file filtered out.
• Existing isMarkdownFilename tests at session-start.test.ts:306–331 already cover uppercase / mixed-case / non-.md / no-extension cases at the helper level. No change needed there.
• brainIndex() and listMd() are filesystem-driven; their case-insensitivity is covered by the existing integration test plus the helper-level coverage.

Out of scope (intentional)

• lib/frontmatter.ts:34, 41 — same kind of endsWith(".md") in the validate-write hook. Different hook, different test surface. Worth a separate follow-up issue; not bundled here to keep the PR scoped to the session-start surface.

Test plan

• npm test in .claude/scripts/: 522/522 (was 521, +1)
• npm run typecheck: clean
• CI matrix green on ubuntu / macos / windows × Node 22 / 24
• Optional manual: create brain/Test.MD in a vault, run the hook, see Test appear in the Brain Topics section

🤖 Generated with Claude Code

[Copilot]

Pull request overview

This PR completes the session-start markdown filename case-insensitivity fix by replacing remaining .md string checks with the canonical isMarkdownFilename() helper.

Changes:

• Updates brainIndex() and listMd() to include .MD / mixed-case markdown files.
• Makes extension stripping case-insensitive.
• Adds unit coverage for mixed-case active work filenames.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 1 comment.

File	Description
.claude/scripts/session-start.ts	Applies case-insensitive markdown detection in brain index and vault listing.
.claude/scripts/lib/session-start.ts	Applies the helper and case-insensitive strip in active work formatting.
.claude/scripts/tests/session-start.test.ts	Adds mixed-case markdown extension coverage for active work formatting.

Comments suppressed due to low confidence (1)

.claude/scripts/session-start.ts:258

• The case-insensitive vault listing path is still untested at the script level: the new test covers formatActiveWork(), while the integration test's vault file listing only encounters lowercase markdown names. Add a mixed/uppercase root or nested .MD fixture and assert it appears in ### Vault File Listing so this call site cannot regress independently of the helper tests.

			else if (e.isFile() && isMarkdownFilename(e.name)) results.push(`./${full}`);

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