fix(windows): repair coder mode input, path validation, prompt rendering and version info

[diillson]

Summary

Windows users hit four independent defects that together made coder mode nearly unusable. This PR fixes all of them at root cause, plus the security gaps a full Windows path-handling sweep uncovered.

1. Coder mode froze after the first message

Typing showed nothing until Enter was pressed. Root cause: the centralized stdin reader polls with WaitForSingleObject, which signals for any console event — resize, focus, mouse — not just keystrokes. The goroutine then entered a blocking console read that stopStdinReader could not cancel, and the orphaned read stole keystrokes from the next go-prompt instance (which is what echoes them).

• The poll now classifies pending records with PeekConsoleInput: only a key-down carrying a character counts as ready, and non-text records are drained so they stop re-signaling.
• A still-blocked read is aborted with CancelSynchronousIo on the reader's locked OS thread — the documented API for cancelling synchronous console I/O. No synthetic input, no console-buffer mutation.
• RestoreCookedMode and resetTTYToSane now have a real SetConsoleMode implementation instead of being no-ops on Windows, so a raw mode left behind by a dirty overlay teardown no longer persists forever.

2. Coder write rejected every valid Windows path

Boundary checks concatenated a slash by hand, which never matches backslashed absolute paths — so anything short of exact equality was outside the workspace boundary. The new stdlib-only pkg/fspath package normalizes separators and compares case-insensitively on Windows, and now backs the engine and both agent validators.

The sweep across all tools also fixed real security gaps on Windows:

• The sensitive-file read blocklist was anchored to HOME, which is unset on Windows — SSH, AWS, GPG keys and kubeconfig were readable in agent mode. Now uses os.UserHomeDir.
• CHATCLI_AGENT_EXTRA_READ_PATHS split on colon, breaking drive letters. Now filepath.SplitList.
• Path traversal detection only matched forward-slash traversal; backslash traversal passed.
• Sensitive-path matching was case-sensitive on a case-insensitive filesystem.
• Command allowlists did not strip backslashed directory prefixes nor Windows executable extensions.
• SystemRoot joined the sensitive-path blocklist as the Windows counterpart of the unix system dirs.

3. Tool args with Windows paths aborted the call

Models emit single-backslash Windows paths — invalid JSON escapes — and sometimes double-encode the args envelope as a JSON string. Both aborted the tool call with parsing errors. RepairJSONInvalidEscapes repairs dirty string literals with an all-or-nothing per-literal rule: a string containing any invalid escape is treated as unescaped, so coincidentally valid escapes inside it (backslash-b in builder, backslash-t in temp) become path separators, while clean sibling strings keep their legitimate escapes. The flattener and the policy normalizer both recover string envelopes, so the security prompt shows real flags instead of a JSON blob.

4. Prompt climbed and left ghost lines; version info empty on go install

• go-prompt skips the wrap-materializing newline on Windows, assuming legacy immediate wrap — but VT-enabled consoles (Windows Terminal, conhost with VT) use deferred wrap, desyncing its cursor model one row per exact column boundary. With the animated live prefix re-rendering four times a second, the prompt climbed continuously and the completion dropdown left ghost copies of the input line. A wrap-aware ConsoleWriter (OptionWriter, gated on VT being active) tracks the cursor column and injects the newline at the boundary, aligning the console with go-prompt's model. The palette overlay also erases the committed trigger line before opening.
• Version displays snapshotted ldflags globals before the update check enriched them, so go install builds always showed unknown commit and date — and one display path had already drifted out of the required call order. The version package is now side-effect free: a single injectable fetch seam, pure enrichment on VersionInfo, and GetReport composing everything order-independently for all three display paths.

Testing

• Unit tests for every fix, including regression fixtures reproducing the exact field failures; red-green verified by reverting the flattener and watching the new tests fail.
• Full suite green; builds for darwin, linux and windows; golangci-lint clean natively and with GOOS=windows (which the native run does not cover for the _windows.go files).
• Known limitation stated in code: resizing the terminal mid-session still confuses go-prompt's frozen width on Windows; that requires the planned TUI migration.

Impact

No API or dependency changes. go.mod untouched. All changes are Windows-gated or behavior-preserving on unix.

[github-actions]

Quality Gate

Result: ✅ all floors passed

Floor	Status	Result	Δ vs main	Budget
1 · Build & Static	✅	go build / vet / fmt / lint	—	—
2 · Coverage	✅	50.6% (bootstrap)	0	≥ baseline
3 · Patch coverage	✅	70.6% (req ≥ 60%)	—	≥ 60%
4 · AI smells	✅	diff scanned	—	—
5 · Scope budget	⚠️	36 files / 1832 LOC (code 1832 + tooling 0)	—	warn 800·25
6 · E2E	✅	go test -race ./e2e/...	—	≤ 15min
7 · Commit lint	✅	conventional commits	—	—
8 · Cyclo (new code)	✅	26 file(s) under threshold	—	≤ 30
9 · Secrets scan	✅	gitleaks	—	—
10 · i18n parity	✅	missing 0, unknown 0	—	—
11 · CRD drift	✅	drifted: 0	—	—
12 · License headers	✅	0 missing	—	—
13 · API breaking	✅	0 incompatible	—	—
14 · Binary size	✅	chatcli 90.9MB · operator 52.3MB	—	100MB each
15 · Provider parity	✅	15 providers · 0 violations	—	—

Config: .github/quality-gate.yml. Workflow: .github/workflows/quality-gate.yml.

[diillson]

Migration note for the intentional API break flagged by Floor 13:

• Removed: CheckLatestVersionImpl (injectable var). It coupled the network fetch, the comparison logic and a hidden side effect that mutated package globals — the root cause of the stale /version display this PR fixes.
• Replacement for callers: GetReport composes build-info resolution, update check and release enrichment order-independently; CheckLatestVersionWithContext remains for plain checks.
• Replacement for tests: inject FetchLatestReleaseImpl (pure network seam) or point CHATCLI_LATEST_VERSION_URL at a test server to exercise the real fetch path. All in-repo consumers and tests were migrated in this PR; a repo-wide grep shows no other usage.