Elide long branch names, and add a hydration reminder - #8

Verify each finding against current code. Fix only still-valid issues, skip the
rest with a brief reason, keep changes minimal, and validate.

Inline comments:
In `@glint.py`:
- Around line 684-689: Update water_reset’s recording path around _load_own_json
and _write_private so --drank preserves the loaded start value but always writes
last as now, preventing stale activity timestamps from affecting the next
render.
- Around line 608-609: Update the hydration state initialization around
prev_water so a missing "water" field defaults to now rather than prev_start,
while preserving the existing handling for states that already contain water.
- Around line 561-568: Update the branch-name truncation logic around the limit
calculation and name slicing to measure displayed terminal-cell width rather
than Python code-point length. Use the project’s existing terminal-width utility
if available, and select head and tail portions so the ellipsis plus both
portions stay within limit while preserving the existing minimum limit and
prefix-favoring behavior.
- Around line 601-615: Make the clock state read-modify-write operation
transactional by using the same lock across the full sequence in both clocks()
and water_reset(). Acquire the lock before _load_own_json and hold it through
the conditional _write_private call, ensuring concurrent renders and --drank
updates cannot overwrite each other; preserve the existing clock validation and
write behavior.

In `@README.md`:
- Line 49: Update the Hydration entry in the README table to accurately describe
the independent water timestamp and reset behavior: replace the “Shares the
break clock” wording with “Shares the break state file; a break resets both
clocks,” and retain the existing --drank behavior description.

In `@test_glint.py`:
- Around line 324-327: Update shorten_branch() to enforce limits using
display-cell width via vis_width(), while preserving the branch prefix and
suffix. In test_glint.py lines 324-327, add a wide-Unicode branch case and
assert vis_width(output) is at most the requested limit. In CHANGELOG.md lines
29-36, retain the “28 cells” claim only after confirming shorten_branch()
measures the retained prefix and suffix by display-cell width.

Verify each finding against current code. Fix only still-valid issues, skip the
rest with a brief reason, keep changes minimal, and validate.

Inline comments:
In `@glint.py`:
- Around line 578-582: Update the loop in the name truncation logic to avoid the
unused `ch` variable that triggers Ruff B007, either by iterating over
`range(len(name))` or renaming the variable to `_ch`; preserve the existing
head_chars and vis_width behavior.
- Around line 842-848: Update the record-reading block around _records to use a
context manager for open, and normalize the selected session_meta payload to an
empty mapping when it is null before calling meta.get("cwd"). Preserve the
existing fallback when no session_meta record exists and the OSError handling
that skips unreadable paths.
- Around line 732-742: Wrap the complete rest_reset read-modify-write flow in
_FileLock(path), including loading the previous state and writing the reset
values, so it cannot race with clocks(). Preserve the existing fallback to now
and the current success/failure return behavior.
- Around line 618-625: Update __enter__ lock acquisition to include O_NOFOLLOW
when opening self.lock_path and use non-blocking or timed flock acquisition
instead of blocking indefinitely. Preserve the existing best-effort behavior by
proceeding without the lock when acquisition is unavailable, while retaining the
current cleanup and return flow.

In `@install-codex.sh`:
- Line 62: Update the CMD construction in install-codex.sh to escape single
quotes in DEST before interpolating it into the tmux shell command, ensuring
paths containing apostrophes remain valid and cannot be parsed as shell syntax.
- Around line 109-110: Remove the `|| true` from the render validation command
in the installation flow so failures from `python3 "$DEST" --harness codex
--width 160` propagate and cause the script to exit nonzero.
- Line 26: Update the --no-rest handling in the argument parser and the tmux
command construction around CMD so GLINT_REST=0 is included in the command
environment when the option is selected, rather than only exported in the
installer process. Preserve the existing command and default rest behavior when
--no-rest is not provided.

In `@README.md`:
- Around line 209-219: Apply the two README documentation fixes: change the
fenced example containing the tmux status line to use the text language marker,
and hyphenate “300-minute window” in the quota description. Do not alter the
surrounding content.

In `@test_glint.py`:
- Around line 399-405: Prevent both render tests from modifying shared rest or
water state: in test_glint.py lines 399-405, add GLINT_REST_STATE pointing
inside the TemporaryDirectory home and set GLINT_WATER=0 in the subprocess
environment; in test_glint.py lines 413-417, isolate build_line’s state with a
temporary GLINT_REST_STATE path or disable both GLINT_REST and GLINT_WATER.