Default bare hunk to diff startup

[tanvesh01]

Summary

• default bare hunk to the interactive diff flow in TTY sessions
• preserve piped stdin pager/patch detection and fall back to help for empty non-interactive bare runs
• update help/docs and CLI/startup tests to encode the new behavior

Closes #116.

Validation

• bun run typecheck
• bun test test/cli.test.ts
• bun test test/startup.test.ts
• bun test test/help-output.test.ts
• bun run src/main.tsx -- --help
• bun test (Bun crashed with a segmentation fault mid-suite; focused tests above passed)

[greptile-apps]

Greptile Summary

This PR implements the long-requested ergonomic default for bare hunk invocations (closes #116): rather than printing help text, a bare hunk in an interactive TTY now launches the working-tree diff UI (hunk diff), while piped/non-interactive invocations still detect patch stdin or fall back to help when stdin is empty.

Key changes:

• New BareCommandInput type (src/core/types.ts): a dedicated { kind: \"bare\" } shape separates the "no subcommand given" case from the explicit --help case in the ParsedCliInput union.
• parseCli split (src/core/cli.ts): bare invocation now returns { kind: \"bare\" } instead of the help text; --help / -h / help continue to return the full help. renderCliHelp is exported for reuse in startup.ts. requireReloadableCliInput correctly rejects bare as a reload target.
• prepareStartupPlan routing (src/core/startup.ts): the bare kind is resolved at startup time via a stdinIsTTY dep-injectable flag — TTY → default git diff startup; non-TTY → pager stdin read, with an empty-stdin fallback to help.
• Tests (test/cli.test.ts, test/startup.test.ts): all four new scenarios (TTY interactive, non-TTY empty, non-TTY plain text, non-TTY patch) are exercised with injected deps; existing tests updated to reflect the changed bare behavior.
• README updated to document the new default UX.

Confidence Score: 5/5

Safe to merge — all remaining findings are minor style/consistency suggestions that do not affect runtime behaviour.

The logic is correct across all four bare-invocation paths and is well-covered by new tests. Both flagged items are P2: a redundant branch that compiles and runs identically, and a dep-injection inconsistency that doesn't affect any current test or production path. No correctness, security, or data-integrity issues were found.

src/core/startup.ts — minor redundant branch and one direct call to renderCliHelp() that bypasses the injection pattern used everywhere else.

Important Files Changed

Filename	Overview
src/core/startup.ts	Core startup routing updated to handle new bare kind — TTY-check correctly gates the git-diff vs pager path; minor redundant branch and one dep-injection inconsistency noted.
src/core/cli.ts	No-command path now returns { kind: "bare" } instead of help; requireReloadableCliInput correctly guards the bare kind; renderCliHelp exported for use in startup.
src/core/types.ts	New BareCommandInput interface and its inclusion in ParsedCliInput union — minimal and correct.
test/startup.test.ts	Comprehensive new tests cover TTY interactive, non-TTY empty stdin (help fallback), and non-TTY patch stdin paths for bare invocations.
test/cli.test.ts	Tests updated to assert bare invocation returns { kind: "bare" } and that --help still produces full help text with all expected sections.
README.md	Quick-start docs updated to reflect new bare-hunk → diff-UI default; --help added as explicit entry point for help text.

Flowchart

%%{init: {'theme': 'neutral'}}%%
flowchart TD
    A[argv] --> B[parseCli]
    B --> C{kind}
    C -- "--help / -h / help" --> D[kind: help]
    C -- "no command" --> E[kind: bare]
    C -- "diff / show / patch / ..." --> F[CliInput]
    C -- pager --> G[kind: pager]

    D --> H[StartupPlan: help]
    F --> N[resolveRuntime -> resolveConfig -> loadBootstrap]

    E --> I{stdinIsTTY?}
    I -- yes --> J["appCliInput = git, staged:false"]
    I -- no --> K[appCliInput = pager]

    J --> N

    G --> K
    K --> L[readStdin]
    L --> M{stdinText?}
    M -- "empty + bare" --> H
    M -- not patch --> O[StartupPlan: plain-text-pager]
    M -- patch --> P["appCliInput = patch, pager:true"]
    P --> N
    N --> Q[StartupPlan: app]

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_{Reviews (1): Last reviewed commit: "Default bare hunk to diff startup" | Re-trigger Greptile}

[greptile-apps]

Redundant else if and else branches

Both the else if (parsedCliInput.kind === "pager") and the final else branch do exactly the same thing (appCliInput = parsedCliInput). Since help, mcp-serve, session, and bare have all been handled above, the only remaining shapes are CliInput | PagerCommandInput, making the distinction between the two branches meaningless.

Suggested change

	} else if (parsedCliInput.kind === "pager") {
	appCliInput = parsedCliInput;
	} else {
	appCliInput = parsedCliInput;
	}
	} else {
	appCliInput = parsedCliInput;
	}

[greptile-apps]

renderCliHelp bypasses dependency injection

Every other side-effectful operation in prepareStartupPlan is routed through an injectable dep (e.g. parseCliImpl, readStdinText). Here renderCliHelp() is called directly, so tests that inject a custom parseCliImpl returning { kind: "bare" } cannot control the help text produced by the bare + empty-stdin path. This is fine for the current test suite (the real renderCliHelp works fine), but it breaks the otherwise-consistent injection pattern. Consider adding an optional renderCliHelpImpl dep, or accepting a pre-rendered helpText string alongside the bare input.

_{Note: If this suggestion doesn't match your team's coding style, reply to this and let me know. I'll remember it for next time!}