fix(callbacks): use . for dots in dict ID callback IDs to fix JSON.parse SyntaxError

[Mukller]

Problem

Fixes #3480.

When a dict component ID contains a dot in one of its string values (e.g.
id={"component": "button.dot"}), opening the app results in a blank page and
SyntaxError: Bad escaped character in JSON in the browser console.

Root cause

In _utils.py, create_callback_id calls x.component_id_str().replace(".", ".")
on every component ID. For string IDs this is fine, but dict IDs are serialized
as JSON. After the replacement, a value like "button.dot" becomes "button.dot"
inside the JSON fragment. The frontend then calls JSON.parse on this fragment
(in parsePMCId and callbacks.ts) and encounters . which is NOT a valid JSON
escape sequence -> SyntaxError.

Fix

For dict IDs, replace . with . (the standard JSON Unicode escape for
U+002E FULL STOP) instead of .:

• . is valid inside a JSON string.
• JSON.parse transparently decodes it back to ., so the frontend receives
  the original dict value unchanged.
• No changes are needed on the JavaScript side.

Before / After

component_id = {"component": "button.dot"}, property = "children"

Before (broken): {"component":"button.dot"}.children
-> JSON.parse throws SyntaxError

After (fixed): {"component":"button.dot"}.children
-> JSON.parse returns {"component": "button.dot"} correctly

Closes #3480.

[Mukller]

Self-Review

Root Cause

escapes dots in component IDs with so they don't collide
with the separator between component-id and property in the callback ID string.
This is correct for string IDs (the JS side un-escapes when splitting).

For dict IDs, returns valid JSON (e.g.
). After , the dot inside
the JSON string value becomes — an invalid JSON escape sequence — and
throws .

Why is the right fix

is a standard JSON Unicode escape (U+002E FULL STOP). It is
valid inside JSON strings and decodes it back to automatically.
The frontend receives the original dict value unchanged. No JS changes are needed.

Correctness matrix

ID type	Value	Callback ID (before)	Callback ID (after)
string			unchanged
dict		— BROKEN	✓
dict multi-dot		— BROKEN	✓
dict, no dot		unchanged	unchanged

What does NOT change

• — unchanged; still used for runtime input matching
• Pattern-matching wildcards (//) — no dots → unaffected
• Multi-output format () — structural separators unaffected
• — still ; callers that parse the JSON portion
  use which correctly decodes →
• No JavaScript changes required — handles natively

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud

[camdecoster]

Thanks for the PR! Our team will review and follow up.