feat: add spintax support for email templates

[anjali20006]

Summary

Adds Spintax support for email templates.

Closes #122

Changes

• Added parse_spintax import in campaigns/tasks.py
• Applied Spintax parsing to email subject and body before sending
• Added Spintax utility implementation in campaigns/utils.py

Testing

• Created a campaign with Spintax-formatted content
• Verified subject/body are parsed before sending
• Confirmed existing email sending flow remains unchanged

Notes

This PR contains only the Spintax-related backend changes and excludes unrelated frontend formatting changes and merge-conflict resolutions.

Summary by CodeRabbit

Release Notes

• New Features
  • Added spintax parsing for email campaigns, enabling subject lines and email bodies to include {option1|option2|...} variants.
  • Parsed output is now resolved into final text before emails are dispatched.

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: defaults

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Run ID: 7f8d5e53-1a26-4234-a8f6-d583b6ed57bf

📥 Commits

Reviewing files that changed from the base of the PR and between d3199b4 and ec55c51.

📒 Files selected for processing (1)

• backend/campaigns/utils.py

🚧 Files skipped from review as they are similar to previous changes (1)

• backend/campaigns/utils.py

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📝 Walkthrough

Walkthrough

A parse_spintax(text) utility function is added to backend/campaigns/utils.py, using random and re to iteratively replace {option1|option2|...} blocks with a randomly chosen alternative. This function is then imported and applied to the email subject and body inside send_email_step in backend/campaigns/tasks.py, after personalize_email and before dispatch.

Changes

Spintax Support

Layer / File(s)	Summary
parse_spintax implementation backend/campaigns/utils.py	Adds random and re imports, a module-level Signer instance, and the new parse_spintax(text) function that loops over {…} blocks containing |-delimited alternatives and replaces each with a random choice until none remain.
Integration into email dispatch task backend/campaigns/tasks.py	Imports parse_spintax and calls it on both subject and body inside send_email_step after personalize_email returns, before the Gmail or mock send path.

Estimated code review effort

🎯 2 (Simple) | ⏱️ ~8 minutes

Possibly related issues

• #210: Directly related — the PR implements the parse_spintax(text) utility and dispatch integration described in the implementation guide for spintax support.

Poem

🐇 A bunny spins words with a flick of a paw,
{Hi|Hello|Hey} — now pick one, that's the law!
With random.choice and a loop through re,
Each email looks fresh, as fresh as can be.
No two look the same, the spam filters say:
"This rabbit's the best at keeping flags away!" 🌟

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 25.00% which is insufficient. The required threshold is 80.00%.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (4 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title accurately and concisely describes the main change: adding spintax support for email templates, which is the primary focus of the PR.
Linked Issues check	✅ Passed	The PR successfully implements objectives 1 and 2 from issue #122: the parse_spintax function is added to utils.py, and spintax parsing is integrated into the email dispatch task after merge tag replacement. Objective 3 (UI preview) is explicitly excluded.
Out of Scope Changes check	✅ Passed	All changes are scoped to backend spintax implementation. The PR objectives explicitly exclude unrelated frontend changes and merge conflict resolutions, aligning with the actual changeset in tasks.py and utils.py.

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✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests

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[coderabbitai]

Actionable comments posted: 1

🤖 Prompt for all review comments with AI agents

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 `@backend/campaigns/utils.py`:
- Around line 23-33: The regex pattern variable `pattern` on line 23 is too
broad and matches any text within braces. Modify the pattern to only match true
Spintax blocks that contain the pipe character (|), ensuring it requires at
least one pipe separator within the braces. This way, only valid Spintax
alternatives like {option1|option2} will be processed, while other braced
content such as unresolved merge tags or literal braces remain untouched and
their content is not accidentally mutated.

🪄 Autofix (Beta)

Fix all unresolved CodeRabbit comments on this PR:

• Push a commit to this branch (recommended)
• Create a new PR with the fixes

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ℹ️ Review info

⚙️ Run configuration

Configuration used: defaults

Review profile: CHILL

Plan: Pro Plus

Run ID: 8370fcba-5e4e-4efd-9dc0-5290da90af70

📥 Commits

Reviewing files that changed from the base of the PR and between 90052f9 and d3199b4.

📒 Files selected for processing (2)

• backend/campaigns/tasks.py
• backend/campaigns/utils.py